Use the following strategies when playing online.

When playing recon, do not be a selfish sniper. Stay relatively close to the objective. You will get more kills and your squad will not feel the urge to kill you as often.
When a vehicle or person is tagged by a tracer round, demo classes will be able to home their rockets in on the target.
Do not be so determined to get someone's dog tags that you forget about endangering yourself or your objective.
Snipers move; it makes it harder for a counter-sniper to draw a bead.
Never get into a helicopter without a partner.