Sometimes your team needs to focus on attacking - if you don't fight then you will lose the game very quickly. However, the last thing you should do is gather in a single location. Take the time to spread out and tackle the enemy from all angles.

As the waves advance, more and more enemies will sweep across the map, including bosses. If you and the other players are tightly bound together, it's easy to get encircled and focus on every attack from all the enemies -- missiles, lasers, all pointing at the team.