1. sub my youtube [ Register or Signin to view external links. ]
2. Post your gamertag and wait for an invite.
3. Join the invite, then backout.
4. Go into split screen with the checkerboard map, and start it. Hit the back button, then A button for instructions:

A button= Instructions.
Dpad Right= 0 prestige.
Right Stick= 1st prestige.
Left Bumper= 2nd prestige.
Y Button= 3rd prestige.
RT= 4th prestige.
LT= 5th prestige.
Left Stick= 6th prestige.
X Button= 7th prestige.
B Button= 8th prestige.
Dpad down= 9th prestige.
Dpad up= 10th prestige.
Dpad left= 11th prestige.
5. End the game, go online and see your prestige.