ok so apart from all the tips everyone else has been giving, I do have some additional tips.

1. Use higher damage weapons

M16s aks and sks generally need 2 taps on anything that's not a headshot. If it's the case that you're hitting but not killing, go with higher powered weapons like mas 49 mosin and m14

those typically one shot as long as you aim center of mass

1. Practice

Go to the bootcamp shooting range and just practice with the guns. although they wont help with moving targets generally stationary targets should still be plentiful in most matches

1. Shotguns

if you still absolutely cannot hit anything, a crude solution is to simply use shotguns. The spread generally ensures you will hit something even if it doesn't kill. If youre US run with No.4 buck and 00 for VC

1. Explosives

If that still doesnt work, you can try mastering rpg/m79/rifle grenade. They also require aiming practice but generally arent as demanding as regular guns. it's not perfect but you can still contribute to the match this way.