(If this is deemed not a good tip, feel free to move it elsewhere)
I have found that a great way to earn xp (especially if you are a player who doesn't always get 20+ kills a match) is to run the support strike package, and have at least the Recon Drone as one of your rewards. The Support Strike Package does not reset on death, so you keep working towards your selected rewards till you get them, and then after you have gotten all of them, it will reset and you can work towards them again. If you are an active player ( Not camping) It is easy to get through all your streaks 2 or more times in a match.
Not only will you get XP for tagging enemies, but you will also get an assist and more xp when a Teammate kills a tagged enemy. If you become good with it, its not hard to have more assists than kills in a match, and still have the highest score on your team.
The controls on the Drone aren't very complicated.
Right Bumper(RB) makes the drone Rise or Ascend
Left Bumper(LB) makes the drone Drop or Descend
Holding the X button will manually exit the drone
Right Trigger(RT) tags the enemy in your sights.
To tag an enemy you need to hold them in the green box that is the Drones reticule, when it turns red you can hit RT to tag them, and then move on to the next enemy. Its as simple as that.
So not only are you gaining quite a bit of XP, you are also helping you teammates locate the enemy. Use this in smaller maps such as Dome to get a good number of tags.