If you want to rack up a ton of kills (and a ton of experience points while you're at it), you'll want to use turrets when you can.
There are two types of turrets on the battlefield. One is the DF.9 Turret. The other is the satellite looking turret called ATGAR. If you know where and how to use these are and how to use them, you can take out tons of enemies helping your team in the process.
The DF.9 Turret can mow down enemy infantry. The ATGAR is useful against other turrets and vehicles and taking those down is going to earn you some nice XP.
Master these turrets and you'll be much more effective on the battlefield.