This is a relatively easy achievement to get. At the end of a battle you can check the leaderboard by pressing RB button at the result screen. There will be a green team (your team) on the left and red team (enemies) on the right. Whoever places on top of those lists on both teams have met the requirements to unlock the achievement.
XP is gained by the following ways, listed in order of most gained to least gained;
1. Causing direct damage to enemy vehicles that you have spotted.
2. Enemy vehicles that you have spotted receiving damage/ enemy vehicles receiving damaged because you tracked them (assisted damage)
3. Causing direct damage to enemy vehicles that your team has spotted.
It's also worth to mention that if you cause or assist damage to vehicles in higher tiers than your own, you will receive additional XP.
The easiest way to achieve the highest are;
1. Pick a tank with a turret. Some armor would be a plus but not a lot of armor that your dependent on the enemy team finding you.
2. Shoot premium ammo. This usually has higher penetration which means more damage caused by you. In the garage press the X button, go to the right twice into supplies and press A, go down one and push Y to switch into using silver. Then select how many you want. Once in a match press A to cycle in between different ammo.
3. Run food. This improves your crews abilities by 10%. That means aiming, loading, and accuracy improve by that much. Follow the same steps as step 2 until your in the screen with the ammo. At the bottom there's 3 slots generally you would run repair kit, 1st aid kit, and fire extinguishers. But pick the food item instead of the fire extinguisher and press Y again to switch to silver.
4. Have a trained crew. The better your crew is trained, the more effective you become. General guild lines says get sixth sense first, brothers in arms second and repairs third.
This method of using premium ammo and food is going to cost you A LOT of silver, so it shouldn't be used all the time.