I think just reading all the post about drift diving here is enough information.
The main thing about drift diving in cozumel is the boats are not moored. They drift, then motor, then drift, and motor to follow the group of divers. The key thing is to keep together with the group. Don't listen to the SB members who say "I don't need a stinking DM to lead me"... It is simply for your safety.
The boat will keep an eye on the bubbles forming over the group, so if you and your buddy wants to stray at a 90 degree angle, they will not follow you.
If your air consumption is higher than the group, signal to your DM when you are down to 1000 psi or so, and slowly ascend, while remaining above the group at a shallower depth. This will assure that when your DM and the maingroup ascend, you will be right above them. The DM will send up an SMB (surface marker) at the safety stop depth, and you will hover below it, and surface as a group. The boat will pick up the main group first, and if you decided to go out on your own, tough luck. Inflate your SMB by yourself, and hope that they can find you.
Another key thing about cozumel diving is to stay close to the DM. He has a light and will point out all of the splendid toad fish, nurse sharks, octopi, crabs, and eels for you. Stay behind him and close to him, so you don't have to fight current to catch up and look at his findings. Fighting currents will burn air, and you will look foolish being the one to force the group to surface early. As many of the good dives start at 90 ft and go shallower, you should have good diving skill, and make sure you let the DM know when you are low on air. Again, the usual protocol is for you and your buddy to ascend to a shallower depth just above the DM, and everyone continue on their dive.