Learn the shortcut keys. For example: X changes your unit formation between line and box formation, and space takes you to your drop zone. Don't use heavy artillery, you will probably get yelled at by teammates. As infantry, use as much cover as possible, trees, buildings, and some roadblocks that are on city maps. Also, at the start of the round, it can help if you wait those extra 15-20 seconds for more reinforcement points to come so you can get that extra unit (4th heavy chopper/heavy tank). It really does make a huge difference.