1. You need 3 other players
2. They need to be decent at Halo
3. They need to be near by as Firefight with lag is pretty much impossible
4. It gets incredibly tough towards the end as your ammo begins to run out and only certain weapons can damage certain enemies. On the last wave we went down from 5 or more lives (I can't remember) to 0 against a single Brute Chieftain (hammer dude) who we couldn't kill with any of our weapons or grenades and had to melee to death.