This achievement is a grind and a half. This solution assumes you don't want to spend money on this free game but I do address how spending cash can speed up this achievement. As always, the choice is yours.
You MUST completely level any combination of 5 skills/perks. So for those wondering you can have 2 perks and 3 skills, 5 skills, 1 skill and 4 perks, etc.
Xbox 360 and the PC version of this game differ somewhat in their set ups and sometimes that leads to confusion in the achievement description.
On PC, you have separate, named crew members for each position in your tank. For 360, it's just one named crew man whom I assume is the commander. While you can technically select the different positions in your tank such as: loader, gunner, driver, etc., each position is considered part of the whole that is your single named crew man. Therefore you CAN train skills and perks that are a combination of the different positions.
For example:
My achievement popped after leveling my 5th skill to full and being offered the choice to choose a 6th. My skill set up was Mentor and Brothers in Arms (which apply to the commander position), Snapshot (gunner), Clutch Braking (driver), and Situational Awareness (radio).
So don't feel you need to train 5 skills/perks to one of the positions available.
As for my setup, If you're only interested in earning XP as fast as you can do the following:
1) Choose Mentor IMMEDIATELY. Mentor adds to your overall xp gain and while it isn't very much you will be grinding out a few hundred matches for the xp you will need. So why not make it easier and eliminate a few of those extra battles?
2) Choose Brothers in Arms Perk. This is the only perk I grabbed (as skills apply benefits while being trained but perks only apply when they reach 100% trained). It increases the effectiveness of all skill bonuses, increasing my bonus xp gained from Mentor by 5%. Once again not much but it saved me at least several extra battles. Although, if I had to do it again I would have gotten this third after grabbing camouflage as the tank I was grinding was detected quite often.
3) This is the last position to boost quickly. After leveling the third perk/skill it takes substantially more xp to level additional abilities. If you haven't grabbed Brothers in Arms by now do so.
4) and 5). These are completely up to you but should reflect your play style. Remember at this point leveling each skill/perk takes substantially more xp. For instance, if I had a good game and received 1,800 xp for my first three skills I would jump 2-4% in their training, but for 4th and 5th I'd get 1% and sometimes none. I would personally go with skills to gain their bonuses as you level them but to each their own. If you're a brawler and like going shot for shot you might want repairs to speed up fixing broken or damaged parts, if you play a tank that's prone to catching fire grab firefighting, if you like to camp and ambush go with camouflage. These three abilities are unique as they are stackable and can be trained for each position of your tank. Meaning, if you really wanted to, you could have the commander, driver, gunner, radio man, and loader all trained in repairs. Throw on the toolbox equipment and a large repair kit and you can autofix tracks in 2-3 seconds.
Some additional tips:
If you don't mind spending the money buy premium and grind this on a premium tank. That's the fastest way to get the achievement.
Make sure the tank you're leveling your crew on is ELITE. If it isn't take the time to research all the packages and the next tier tank to make it so. ELITE tanks gain crew xp equal to the xp earned for the tank itself, and this is before Mentor and BiA is applied.
If you don't need to save the silver invest in buying the premium rounds. You're grinding for xp, the better game you have the more you'll get, so buy those HEAT or APCR rounds. The more of a contribution you make to your team, win or lose, the more xp rewarded at the end.
Take advantage of the bonus xp events which you can check out at the World of Tanks homepage or during the server selection screen at start up. Don't miss out on your daily 2x XP for your first battle of the day.
DON'T SWITCH YOUR CREW OUT. Unless you have the gold to 100% train your crew don't switch them out. You lose time retraining your crew on their new tank just to get them to the level that they begin learning skills and perks again. It's a waste of time and is only effective if you have two premium tanks (paid with gold) that you juggle your crew between to get the daily bonuses. However, even with premium transfers the veteran crew must be trained initially.
Just because I remember them as premium, take the Locust and the T14. Both are Tanks that you can only purchase with gold and come with 100% trained crews, which means you can start them on skills and perks immediately. Now you must pick one of their crews to dismiss as you will be jumping a single crew back and forth between them. Say you remove the crew of the T14 and assign the Locust crew to the T14. The Locust crew will remember they are 100% trained on the Locust but will need to be 100% trained on the T14 before skills and perks become available. If you have deep pockets this is the fastest method as it allows you take advantage of multiple tanks' daily bonuses, as much as your checking account allows, and by spending more gold you can 100% train the same crew in each tank you're transferring them to, however, this ONLY APPLIES TO PREMIUM TANKS. ELITE tanks do not have this privilege and their crews are much dumber, forgetting their training on their original tank when you try and transfer them back. I attempted this with two ELITE tank crews. I transferred my KV-1 crew to my KV-1S and trained them back to 100% to keep leveling skills/perks, however, I thought surely as it was the same crew they would know how to operate their old KV-1, but when I transferred them back I had to retrain them back to 100%. So please consider the stupidity of your tank crews when moving them around.
If you have any questions or think something should be added to this solution please leave a comment.