Hmmm, don't rush like a stupid idiot (like you do in cod....), check your corners when you are moving, Don't FULLY spray if you have an automatic weapon, burst insted, because there is something called SPREAD, which does NOT exist in cod.
Try all different attachment's to find "your" speciall attachment, to see which one you like the most. Try to use all different weapons aswell, ect ect.
My facourite is the M249, Foregrip, Extended mag and Kobra (RDS)