Don't forget the value of semi-automatic fire in certain situations, but by that same token do not overuse it. Practice when to use semi-auto, when to use burst auto, and when to just mash down that fire key. The only time you should be doing the latter when using an assault rifle is if you are in a point blank range fight with an enemy soldier.

At short to medium range, automatic with burst fire is typically the best. You need to learn to time your bursts in such a way that you get 3-4 shots in, then rest and get 3-4 more shots in once the gun stabilizes. Quick, short bursts are key to eliminating hostiles quickly and efficiently.

Also remember that prone is highly overrated and often overused by new players. Going prone results in a huge deviation for a few critical moments before it becomes even as good as crouching is. If you encounter an enemy as you run around a corner and are finding yourself wanting to go prone and then fire, you are making a critical mistake that many new players do. In any fluid combat situation where you must quickly fire at your enemy, and you are standing, you should crouch rather than go prone. Your accuracy will immediately increase and you will find it far more effective then leaping to prone and then firing. Prone should only really be used for taking cover, crawling into positions to remain unnoticed, or when you are firing from an entrenched position that you've had time to hunker down into.

Another thing that might be killing you in two shots is a shotgun, though you'd likely recognize the distinctive noise unless it is a very loud firefight. Beware anyone using a shotgun, and keep your distance from them. These babies can be one shot kills at close range, which nullifies your ability to fight back. Also, look out for rockets, and get your rocket unlock when you can - they're one of the most useful tools on the battlefield other than the defib.

Also, neither the Voss nor the Baur are really better than the other. Preference plays a role, but a general rule of thumb to remember is what Rage brought up - Voss for close to medium range fights, Baur for medium to long range fights.