With practice. Try to maximalize all of te classes as soon as possible, and use them as they should be used. I mean try not to rush with the covert ops, try to explore all the mines with it (with binocular) and us the stealth. Try the sharpshooting.
Rush with the soldier, it has no other point for me, just the kill them all type of game.
But in generally, if you want nice scores at the end, "use" your mates; dont fight alone, follow someone, because 2v1 is always better.