You Sneaky Bastard!
Being the coward you are, Active Camoflage is your friend. If you crouch down and stay really still, it's the perfect way to avoid detection if you want to stay as far away from the conflict as possible. Just keep an eye on your radar and if anyone's coming close to your hidey hole, hit the left bumper and go invisible. With any luck they'll pass right by you without so much as a shot fired.
If by some miracle you muster up the courage to actually make a strike, equip yourself with some Plasma Grenades and perform stealth stickies on folks who ignored you earlier. It's silent, it's deadly, and it's pretty much a guaranteed kill if you land it directly on someone. As a side-bonus, this strategy can be used to great effect in objective matches where opponents pause to capture territories or pick up flags.