All credit goes to Nak3d eli and his amazingly helpful videos. Although I currently have not completed the campaign on legendary difficulty I am breezing through it with this guy's help.
I also first completed the campaign on heroic to help me get a feel for both the game and the enemies.
This is for those of you who have already completed the game but really want to do it on legendary both quickly and effectively.
Subscribe to Nak3d Eli's halo channel here:http://www.youtube.com/user/Nak3dHalo?feature=watch