Practice. Play the game. I never found anything quite that effective. But if you really want to, I'll tell the same thing as always.
Aim smoothly. Get used to not jerking around so much. A lot of guns are automatics in NS, and there is no kickback, so simply tracking the target is often the thing that is the difference between a kill and a death.
I did this by drawing lines on walls with my LMG when I was bored in MS......it's easy to see how you aim when there are bulletholes everywhere you point it.
After you get good at that, try to aim down a hall and simulate the movements of a skulk bunnyhopping as it comes at you. Hold down trigger.
For the erratic skulk movements? Spray and pray. >_<
That's what I did. I think I hold my own well enough, but I still think that if you have time for this, you have time to play the game more, and do some real work. It's always best to train under pressure.