My tips:
In halo one I rammed my sensitivity right up to 10, it allows for faster accuracy, a decent edge over the default sensitivity 3 guys... but in halo 3, 10 is so damn fast I've settled for 5.
Change your controller set-up to BOXER: switching grenade and melee buttons so you have way more accuracy to move and melee with the left trigger.
I still need to get good with the BR though, and the sniper.
Oh if anyones of similar skill level pls add me:
Name: SinkRox
EXP: 80
http://www.bungie.net/stats/Halo3/Ca...player=SinkRox