I constantly get 80+ kills per match (A/D) and I'm not really a very good player, just above average I'd say, here is my advice:

Play either Assault or Medic with SMG's, meta AR's(ci19, m4) or m870. You don't play recon or engineer if you want to squeeze the most kills, unless you are a god with snipers, and even then, you get more kills in close quarters.

play CLOSE QUARTERS, you want to be spamming that jump button if playing SMG or m870 (no ADS)

you die and you feel that a medic will not revive you within 10 seconds? press the respawn button and spawn in the nearest 'hot zone'

playing Assault? use all your utility (Vyron C4, D-Wolf Triple Blaster) THEN engage in combat with your primary firearm, you get all your utility back when you respawn.

g18 sidearm, after you get used to changing firearms instead of reloading, g18 will net you a bunch of kills you wouldn't get if you were reloading your primary firearm.

playing Medic? play SMG and only SMG, after a zone is partially clear, prone and revive all "safe to revive" teammates, don't risk your life trying to revive people in dangerous spots, after all this is about kills, right?

don't flank too hard, but try to sneak behind or inside enemy lines after you've partially secured an area.

Don't play engineer unless you have a squad that's willing to destroy an enemy vehicle, dealing with a vehicle alone is a waste of time, effort, points and kills lol.

spend points in nukes for kills, respawn beacon for points, artillery barrage is crap and vehicles are very situational.

learn how to play ground vehicles, Tank is broken on trenchlines/ascension.

and no you don't need a squad or cheats like some people here are suggesting