Hints:
The Ammo Regen power-up is the perfect complement to the Prox Launcher use it to sow mine fields in areas you know your opponents will be headed. Try to place those mines in hard-to-spot locations, such as on walls or doorways, so the intended victim won't see them in advance and detonate them with a rocket. Be sure to bind keys to critical team commands so you won't have to hit Esc and issue orders from the menu. This saves you much time and allows you to keep moving while communicating with teammates. Most of the time you'll want someone who's guarding your base to grab the Doubler power-up, but you should let your offense use it in the Overload game mode so they won't have to spend as long firing at the enemy's obelisk to destroy it.