Agreed with the bounties and moving the gun between characters to level them. Anytime you have a bounty to get a certain amount of kills then load the Mars [b]Exclusion Zone[/b] mission and increase the difficulty. Kill the Cabal wave and except for 1 and let him kill you so you start the wave over. Higher level enemies, especially ultras and majors, give you more XP (and you'll be glimmer farming at the same time).