Halo 3 Multiplayer Help?

I just bought my xbox 360 slim 250 gig, and I finished the campagin in halo 3, and I play alot of match making, then I made my own stage, i try to invite my friends and everybody, but no one ever joins, not a SINGLE person, can someone tell how I can get ALOT of people, try to be as detailed as possible in yur answer, thanks to everyone who tried to help me