How do you get EXP in Halo 3? Please Help?

[idk]

I have beaten the game on normal.

found 10 skulls.

i also have won matches on live on social slayer and skirmish.

i also have ODST helmet.

but i have ZERO exp??!?!?!?!??!?

i also have been mvp and gotten medals and have been the top player??

how come i have no exp?

i sometimes leave the match early and have betrayed my friend only once



PLEASE HELP

 

[Miner40whiners]

well most of all win alot of ranked matches, and when you leave a match you lose alot of exp, and another reason why your not getting exp is that you didnt follow the user agreement and they stopped you from getting exp for the month