Bored with my classes on MW2?

I'm always changing my classes because if I use one for too long or overuse one, I get bad with it. Can you please post some advice below (Classes, Weapons, Perks, Attachments, Equipment, Tips, Strategies, you know.), cause some of my classes that I'm getting bad with used to get me Harriers, Pave Lows and Predators every game.