The goal of the game is to break all of your team-colored monuments (obsidian blocks and others, look for blocks with particle beams above them before game) before others do. The team that has no monuments left to break wins.
Unlike Dual, which is written above, it is best to be rushing most of time. Bring some people near you and hit other's bases in groups — this will be hard to deflect for one person that may have respawned. But if you respawn and see someone breaking a monument behind you, and there is a chance to defend — do it. This will at least stun breakers team while your teammates may be finishing breaking last monuments.