Note: I am assuming you are playing this on normal. If you play on Heroic or Legendary there will be more enemies and some will spawn in the spots I say to go.
When you first start out you'll have a DMR and Assault Rifle, you'll see 4 grunts hopping over a barricade in front. Take out the grunts and run up the left side, you should then be above the battle, throw your 2 frag grenades into the midst of the fray and then backup into the doorway to get 2 more frag grenades (and a health pack if needed). Continue clearing out the guys and a dropship will come in with more people. At the end of the leftside walkway that your currently on you will find a sniper rifle which can also be of help. After clearing out the area you will recieve the Target Locator and can switch to armor lock if you want.
Current Weapon: DMR and Target Locator
Once you have the target located you will be faxed with 3 grunts, 1 elite, and 2 wraiths, you can use the target locator to take out the wraiths or run up to them and hop on to destroy them that way.
NOTE: On normal difficulty the target locator ammo will slowly regenerate.
Current Weapon: DMR and Target Locator
After everyone is cleared you will notice a rocky outcropping on the right side, there will be a rocket launcher with 4 shots there (leave it for now). Once you recieve your warthog you will head to the AA gun (right side). You will run into a small group of grunts and a ghost on the way but your warthog can handle them. Once you hit the AA gun continue clearing out the area while making your way up top, with your target locator feel free to use it on the dropship. You will have to dispatch a few Elites, alot of grunts, and a few ghosts.
Current Weapon: Target Locator and DMR
Upon activating the AA gun you will then recieve another warthog, push on to your next objective where you will again run into 2 ghosts, 2 - 3 Elites via dropship and a detachment of grunts, you can take them out or just push through and not worry about them.
Current Weapon: Target Locator and DMR
At the next spot you must turn on the power then the satelite to establish contact with HQ, you will also have to take out a Revenant, quite a few elites, a few jackals and grunts. By the Jackals there is also a sniper which is a great way to take out the Revenant. Once you have cleared the area, turn on the power, walk right outside and stay on the balcony, when you see the dropship come in and start to deploy use your target locator on it, if timed properly, you will destroy all enemies (minus one grunt) that drop from the ship and net yourself a Killionaire.
Go over and turn on the Satelite to establish your cotnact, then come back and on the 2nd floor you will find a rocket launcher, exchange it for the DMR and head over to your new Gauss Warthog.
Current Weapon: Target Locator and Rocket Launcher
As you head back to base you should be able to easily dispatch all enemies and vehicles with the Gauss Turret. Once you have cleared the area, go pick up that rocket launcher from before on the rocky outcrop, you should now have a target locator with 1 or 2 shots, and a rocket launcher with 8 total rockets.
Current Weapon: Target Locator and Rocket Launcher
Head back in and open the gate, once you open the gate you will see an Elite lead a rush towards your position, use your target locator in that corner area you saw the elite come out out, this should take out all enemies and net you another killionaire.
Head up the hill then you will see that the garage bay doors have been opened and you have 2 grunts, an elite, and 2 hunters waiting for you. as you head in you'll see two pillars at the front of the bay, you'll notice frag grenades, a medkit, and shotgun. Swap your target locator for the shotgun.
Current Weapons: Rocket Launcher and Shotgun.
With your fully loaded rocket launcher you should be able to take out both hunters, if at all possible hit them in the back, be mindful of their cannon and just play it smart, this should be a fairly easy fight. You can then use your shotgun to mop up the remaining Elite and Grunt if they aren't already dead. If you use up all your Rocket Launcher feel free to swap it for one of the covenant weapons or just hang on to it, your call.
Current Weapon: Shotgun and Rocket Launcher / Covenant
Once you take the elevator upstairs, you will enter a room with 3 grunts at the end on the right and 1 Elite on the left, one frag grenade to the grunts should dispatch all and a few shotgun blasts makes quick work of the Elite.
In the next room you meet back up with your team, help them clear out the jackals in the bottom room and the elite, you will then keep pushing trying to go up to the very top, you will run across some Elites, Jackals, and grunts. If you play it smart there shouldn't be any problem till you get ot the very top. At the top you will have a contingency of Grunts, Jackals, and 1 Gold Elite and a normal. If I have any rocket ammo left I will use it here, otherwise try and use some well placed grenades and shotgun to take them out. As soon as you get across there is a healthkit so if you need it use it.
Once you have cleared the floor you will head through the doors to the end of the level, right before you pass through the doors you will find some rocket ammo on the right, so if you still have yours you can pick up more ammo there. You will need to take out both Jackals, you will then see a dropship come in and drop off 2 cloaked Elites. The rocket launcher should make quick work of them. There is rocket ammo everywhere here, so use it constantly.
After both elites are dead, you will then need to take out Banshees and the covenant dropship using the rocket launcher, it will auto home in after you establish a lock. Have fun blasting them out of the sky.
Congratulations, level complete.