1.) Move while shooting. A lot of you freeze when you start shooting. Now if the enemy hasn't seen you standing still can help you land that extra shot, but as soon as your opponent has spotted you and starts returning fire you must immediately start zick-zagging towards him. Why towards? Well in the case that you both end up with an empty clip you want to be in range to melee him - which provided you hit him once or twice, will kill him.
2.) Don't queue in a corridor. Tight space leave you a sitting duck. If a friendly is in a corridor and you want to go through - activate armour mode and run past. Don't stand behind him. Ideally you want to avoid corridors and flank.
3.)Don't chase people around corners. If you shoot at an opponent and he runs around a corner he will be waiting for you. This is where you need to ask yourself - Can I flank? How much health does he have left? Is he alone? If you can flank, then flank. If you hit him a few times and he is close to dead, enable armour mode and run around that corner, maybe jump around the corner. If you suspect there might be more than one opponent there, chuck a grenade and move on. You might get one kill if you rush around the corner, but if you play it safe you can spare yourself a death and get one step closer to that Ceph gunshipt or Maximum nanosuit.
4.)Wean yourself off AA. It is a waste of a perk slot. It often activates too early and slows you down. Many players die with their backs to me because my first hit activated their AA and they were stuck trying to "walk" behind cover.
*I do not support bunny hoppers. Its a pathetic game exploit and if you bunny hop you svck.