I won't lie, your grenades are, sadly, close to useless in this game. Not to mention that you need to choose them from your weapons separately (yep, you are no Master Chief). They behave like rubber balls in their physics. Using them for pin-point explosions is close to impossible and I strongly recommend you only use them to force enemies into, or out of cover, and giving you a short time window to make a run for them before they shoot you to pieces.
Cover is your best friend. Stay in cover using only potshots and never expose yourself longer than needed. On Veteran, enemies kill you in two hits with no chance to break free, basically meaning that you are dead after the first hit. Spray and pray won't even get you past the first level, so become a god at iron sight aiming! Being fast will also help you tremendously.
Normally enemies drop health packs, but on higher difficulties I never found any. This means that having low health early on in the level is, most of the time, a certain death penalty. Try to not get hit at all, your life will become easier, and most importantly, you will last much longer.
Your basic weapons are good, but ammo might be an issue in later levels. Try to conserve ammo and, if needed, switch to the German weapons. Having an empty weapon is never a good thing.
You can start the game outright on Veteran difficulty. However, this is really tough and I do not recommend this if it is your first time playing through. You might know other Call of Duty parts, but this one has a really tough Veteran difficulty. So with that said, I've split it into two playthroughs. However, if you feel like you're ready for veteran, skip to the lower part where I give detailed information on each level.
Story on Greenhorn
Start the game up as normal and as soon as you finish the training, you will get your first achievement.
Now you will start on the level Pathfinder. Here you can get two achievements. The first would be to finish the level while only using your pistol. This is really easy since there aren't that many enemies. Just kill what you have to and DON'T use your melee or grenades. As soon as you're done the achievement will unlock.
Pea ShooterComplete a mission using only a pistol and no melee attacks.
If you managed to stay alive through the whole level, you will earn another achievement for doing exactly that. However, I'm certain that if you don't get it here, you will get it while going for the next achievement.
SurvivorComplete a mission without dying or loading a checkpoint.
We will now reload the start of the mission. We will have to get a kill with each of the following weapons : Pistol, Rifle, MP and grenade. This may be easy, but keep in mind that you will have to SURVIVE the whole level without dying once. Luckily the first level is a cake-walk with every weapon, so upon finishing it, you will get the following.
GunslingerGet kills using a pistol, rifle, submachine gun, and grenade in a mission without dying.
We'll now play through the campaign which isn't too demanding on Greenhorn. As soon as you free the Captain out of the detention camp, you will get your next achievement
Continue playing through the Campaign and upon finishing the mission on the ship, you will unlock the following achievement.
Continue playing through the campaign and upon finishing the second tank level, you will unlock the following achievement.
Finish the next level where you have to infiltrate the tank facility and upon finishing you will unlock the following achievement.
Play through the snow level with the sniper and as soon as you exit through the bunker, you will get another achievement.
It's time for the last level! Hoist the flag over the Reichstag, and finish the game. Now that you've beaten the game once, prepare for the last few achievements.
Story on Veteran
I will provide as many tips as I can. You WON'T get additional health during missions like on Greenhorn and your AI partners WON'T suppress enemies as much as they did previously. Around three hits will kill you for certain, not to mention explosives, snipers and MG's. Stick behind cover as much as you can and only lean out if you plan to take pot-shots. I wont lie, the lack of additional health packs makes this game really tough on Veteran, not to mention the insane accuracy of your enemies.
Level 0 : Training
Follow the instructions and you will finish this level, no need for further explanations.
Level 1 : Pathfinder (Part 1)
This will be the first real mission. Kill the urinating guard, head forward and kill the enemies in the bunker. Place the beacon and run immediately to the house front ahead. Kill the heavy MG so the soldiers can advance and fight your way through the buildings. Careful, there are a few enemies that will shoot from upstairs, out of windows and behind boxes. Advance slowly and kill everyone you see. Upon reaching the trenches, the level ends.
Level 2 : Pathfinder (Part 2)
At the start, make sure to kill the MG gunners early on and as soon as the last one drops, make a run forward to the wall (if done correctly, no enemy will hit you). Head in the backyard to crawl through a hole in the fence (surprise attack on the enemies behind it) and lob a grenade to dispose of the half-track gunner. Now head to the left, across the wall and clear the building. Throw a grenade inside to check if they really are dead and head to the backyard. Work your way to the right along the left side of the area to circle the heavy MG. Kill the remaining forces and kill the enemies around the AA gun. Place an explosive and continue to the next one. Clear the trenches first and advance carefully to the right to flank the remaining enemies. Blow that one up and follow the path through the house to the third one. Be careful of enemies to the right (dispose of them first). There will be an MG gunner to the right of the AA gun, so take him out fast, if not first. Mission is finished as soon as you blow up the third AA gun.
Level 3 : St. Mere Eglisee
Head in the building straight ahead and kill the enemies until the tank arrives. Head to the church and claim the Rocket Launcher to destroy it and defend the church against the enemy onslaught. Grab a Rocket Launcher and get to the next marker. Upon getting close, mortars will income so get back and destroy the tank that breaks through the debris. Head towards the next marker on your map and stick close to cover. Be careful of enemies on your way, always stay on your guard. Get the Sniper Rifle near the wall (be quick, you are a live target there!) and kill all the enemies. Dispose of the Mortar crews to finish the level.
Level 4 : Route N13
This level is straight forward since the only times you can die is when Kübel Wagons attack you (take out the drivers) and when you have to defend your friend. Head to the upper floor to defend him and finish the level as fast as you can.
Level 5 : Brecourt
Follow the Captain and take the route to the right. Dispose of the MG gunner and move into the trenches. Now move through the trenches and watch the turrets go boom one by one. Be careful of MG gunners, so advance slowly rather than rushing. As soon as you find the traumatized medic, give your Sergeant some covering fire. If you don't keep him alive you will need to get out and grab his explosives and believe me, you don't wan't to do that. Blow up turrets as you pass them, head through the barn and get inside the house. If you are no good with the MG emplacement, DON'T use it, instead wait for them to come in and kill them as they enter the house. This will happen once you pick up the second document. As soon as every soldier is dead, the level ends.
Level 6 : Chateau
Although this level might look tough on first look, it really isn't. Simply take your time while advancing through the corridors and make sure to keep an eye on upper ledges and doors. I recommend using the BAR for the majority of the level.
Level 7 : POW Camp
This is possibly the hardest mission in the whole game because it's timed. Not to mention that you have to enter it to free someone, you will have to leave it as well in a really short period of time. The 10 minute timer will start as soon as you shoot the first round. Stick to cover but you'll need to rely heavily on your teammates, otherwise it's impossible to make it in time. Be careful of enemies bursting through doors and be prepared to spray them with your Thompson at any time.
Level 8 : Pegasus Night
Upon deployment, try to take the MG nests out as soon as possible. Head to the bunker and support your men getting across the bridge. Now, as soon as the last one is across, go yourself (be careful of any remaining enemies). Take cover to the left and advance to the other side to get to Sgt. Miller. Support him in every way possible and use the big gun to destroy the tank. Clear out the remaining enemies to finish the mission.
level 9 : Pegasus Day
This mission is really tough, and sadly there isn't much cover either. Stick to the booth in the middle of the bridge and kill the enemies on the other side of the river. As soon as your men are back, head inside the bunker and wait the remaining time out. As soon as the timer runs out, kill the remaining enemies and finish the level.
Level 10 : Dam
Head across the dam and snipe every visible enemy. Blow up weapons as you go along and as soon as you destroy the last one, the door to the dam will open with an enemy. Inside the dam, do the same as in the villa, just watch the corners really carefully. As soon as you blow up the last turret, you will have to head back through the dam. Careful since there will be a lot of enemies waiting for you. As soon as you reach the top again, a truck will be waiting for you.
Level 11 : Truck ride
Try to aim with the Panzerfaust a little ahead of the cars. As soon as you reach the bridge, make sure to snipe everyone that wants to cross. You should use the rockets on the cars and the Bren on the bikes, but its totally up to you.
level 12 : Airfield
As soon as you reach the Airfield, be prepared for a really tough part. Shoot the incoming transporters as soon as you see them and destroy the planes. Now jump off, kill the guys on the roof and enter the AA gun again. Use the sand barriers to take cover. This is the only way you can do this. As soon as it's done, enter the car again, head to the plane and leave.
Level 13 : Ship
Follow Price and make your way inside. As soon as the shooting starts, grab all the weapons and explosives that you can. Make your way through the corridors and kill everything you see. Be careful upon leaving to go to the hangar, there are a lot of enemies waiting for you. Always make quick shots, never stay too long outside and be aware of enemies above you as well. Always be on your toes and be very thorough with your sweep through the corridors. When you're done, head carefully to the boat.
Level 14 : Stalingrad
This level is straight-forward, since most parts are scripted. Simply follow the instructions and you should be fine.
Level 15 : Red Square
Your biggest problem in this mission are the MG's. Carefully go from cover to cover and pick off single enemy targets. As soon as you reach the fountain, head to the wall, kill the enemies behind it and keep killing through the corridors. Once on the upper foor, pick the Sniper Rifle up and pick off the Officers (two in the trenches, two near the building's stairs). Get down, wait for the tanks to get blown up and head through the underground. Enter the destroyed building and as soon as you reach the trainyard, the level will end. Be careful as there are a lot of enemies between you and the train yard.
level 16 : Train Station
Keep the Sniper Rifle at all costs since this will be your main weapon throughout the level. Make sure to pick off the MG gunners from distance and you shouldn't have any problems at all. Avoid direct contact with enemies as much as you can and try to snipe their feet while crawling underneath the train cars. This will keep you out of harms way most of the time. As soon as you are behind the enemy lines and reach the statue, the level is done.
Level 17 : Sewer
Again the sniper will be your best friend here. Play this level as you played all the levels with confined spaces and you shouldn't have any problems at all.
Level 18 : Pavlov
This mission is really tough. Provide covering fire for the idiot and kill off the snipers (they spawn randomly, make sure to get them with the third shot because with the fourth, they will aim and kill you 99% of the time). Now work your way carefully around the left side of the destroyed wall and enter the building. Clear the building out VERY carefully and make sure to destroy the tank as soon as possible (the best chance is when it arrives). Now the timer will start and your best bet will be to hide close to the stairwell, with a solid wall and NO second stairwell behind you. Shoot everything that dares to come up and as soon as the timer is done, you'll have completed one of the hardest missions in the game.
Level 19 : Factory
In comparison to the previous mission, this is a cake-walk. Make sure to let your partners handle the tough bits, use your Sniper Rifle and cover wisely. Like i said, a cake-walk.
Level 20 : Railyard
This level is also pretty straight-forward. Simply shoot the enemies from underneath the train, this will prevent you from being shot at most of the time. Pick off the enemies inside the rail yard slowly since they really like to camp on you. Kill them all to finish the level, easy as that.
Level 21 : Tank Drive Country
This is really easy. Your tank can take around three hits and enemy tanks take around two, most of the time. Luckily, the rounds fly in a straight line, so simply aim and fire away. However, there will be infantry scattered throughout the level with Panzershreck's which will be your biggest problem. Simply kill them by shooting behind them (splash damage for the win).
Levle 22 : Tank Drive Town
Same as the previous level, just a little bit shorter and more enemies will shoot from inside the buildings.
Level 23 : Hurtgen
This mission is also straight forward. Through the snow you can see almost every enemy from quite a distance, so use that to your advantage. Make sure to keep a Panzerfaust on you to dispose of the tank that will come a little ahead. If one round isn't enough, make sure to pick up a second from the bunker nearby. Clearing out bunkers is essential in this level, so do it. As soon as the Panzer is done, the level will end.
Level 24 : Rocket
This is rather easy if you know what to do. Take it slow and snipe everyone you can. Sadly, you won't find any ammo for the Sniper Rifle in this mission, so make sure to make every shot count. Enemies tend to appear out of nowhere, so always be on your guard. Clear out bunkers whenever you can and as soon as you meet up with your squad, take the left path. Make sure to clear out the MG gunners first and kill off one enemy at a time. As soon as you're done, i'ts time for the last mission.
Level 25 : Berlin
Work your way through the streets with your Sniper Rifle until you hit the tank. Make sure to kill the gunners and enemies first, and avoid the tank along the left wall. Destroy all the Flak tanks and storm the building with cover from your tanks. Now enter the building, reach the roof and finish the level.
Upon finishing the last level and planting your flag above the Reichstag, the mission will end. Congratulations, you now have beaten the game and earned the last achievement
War HeroComplete the game on the hardest difficulty.
Here is a video guide for all the levels, credit goes to matt bass.