In Halo this is a huge tactic for Free For All. In Halo 3, the rankings system worked uniquely in that you had to also have a certain ELO rating (highest skill) in addition to normal exp from playing games. I got my "rank 50" in Lone Wolves (subsequently my friend carried me in doubles lol but my own 50 was FFA). The winning strategy was to camp the area on a map where the power weapons spawned and just clear it out over and over. For example on Guardian i would patrol the shotgun hallway-> active camo/yellow lift and top blue room. On The Pit I would pick a sniper tower and patrol the base on that side and the tower, while occasionally glancing towards sword. On Narrows i would try and control the middle of the map but there were a lot of egress points so I'd usually die a lot but also get lots of kills. On Foundry I'd get sniper+ BR and stand on the crates in the back opposite the sniper and spawn kill people on the ground floor. On High Ground I'd grab camo and rockets and patrol the cave area to bridge. On Snowbound I'd grab beam rifle and carbine and try to lock down the top of one of the towers.

Man i loved halo 3. Anyways, that's my strategy on most singleplayer fps games when you don't have teammates to help OR worry about.