Haven't played for quite a while now but when I did play I played as the Vanu, mainly Engineer and also used the Scythe and the Magrider ( both with some good upgrades + weapons ). First thing to do IMO is upgrade your main infantry classes weapon, I basically did that first, all of the upgrades I wanted for my gun, the reflex sight, advanced forward grip and the compensator. Also good idea to grab the 1 cert stuff you want during that time.
After that I say get more skills. Playing mainly Engineer I got the proximity mines and they are pretty much trolling 101, I have had massive kill streaks from controlling alleyways, doorways and general building areas, putting two prox mines down at different spots where you know enemies will come, if you're good at aiming you'll rack up a good amount of kills, gun and mines combined. Before they fixed some stuff you used to be able to throw the proximity mines through the spawn forcefield, that was hilarious, especially when you had the enemy pinned inside the spawn and there's 10 of them at the doorway shooting through thinking the enemy can't hurt them, until a prox mine comes flying in and blows them to fucking pieces.
AV mines are useful too though they certainly need more practice with placement and I liked to use them when I haD sneaked in amongst the enemies, putting them behind the enemies battle line so when their damaged veichles retreated to repair they'd naturally roll over a mine.
This is of course all irrelevant if you don't play engineer, lol. As long as you don't play a bundle of sticks sniper we can still be friends.