Suggestions? Well, here are my suggestions (but only because you asked):
1) Prepare to have a ton of fun.
2) Read through some of the thousands of previous posts in the Cozumel section. There are hundreds of threads on which dive ops to use and which restaurants to eat at. (be sure to try Guido's)
3) Read the thread on Drift Diving in Cozumel.
http://www.scubaboard.com/t77908-.html
4) Plan to use bottled water for many things, just to be safe. Yeah, I know, most reputable restaurants and hotels blah blah blah.
5) Tip your Dive Guides. They take care of you, you should take care of them.
6) Take nothing but photos and memories, leave nothing but tips and bubbles. In fact, take LOTS of photos.
7) Even if you are staying at an AI resort, try some of the great restaurants on the island. Really. You have to. It isn't the LAW, but it should be.
8) If you are shopping, don't be in a hurry. Similar merchandise can be found at many places, and some are better priced than others. In general, the further away from downtown, the lower the prices. (Similar "rule of thumb" for smaller restaurants.)
9) Ask locals for advice on restaurants also. This includes the dive shop staff. Maybe they will send you to a relative's restaurant, but they want you to enjoy yourself so that you will tip them well! You did take care of them, right? The locals can't afford to eat at Primo's and La Mission all the time, so they often know the "econimicas", the reasonably priced, good quality places to get food (like Las Palmas).
10) Drink alcohol judiciously, drink bottled water generously. get enough sleep. Protect yourself from the Sun.
11) Dive smart, but dive, dive dive!
12) Remember that gloves and knives are not permitted in the Parque Nacional (sp?). The exception on the glove rule is at the wreck. Some dive ops are more lenient than others, but they really are not permitted.
13) Bring a dive light on all dives if you can, even daytime dives. The colors get muted at depth, a light will really bring out the colors.
14) You know the one guy on every dive boat that is a PITA? Don't be that guy. Don't be the last one ready to jump in the water. Don't rush, but don't hold up the group. Be helpful, or more correctly offer help if appropriate, but don't be arrogant. No one likes a "know it all". Be a good ambassador for your country, and respect theirs.
15) Follow the Dive Guide's directions. If you don't understand or you don't agree, ask for clarification if time permits (see #14). Don't blindly follow, don't do "trust me" dives, but don't ignore either. Some of them know quite a bit.
16) On drift dives, stay behind the guide. They often find great things and it is a pain to try to fin against the current to go see whatever they have found.
17) Relax and enjoy. Everyone else will enjoy you better and you air will last longer.
18) Be a good buddy to your buddy. 'nuf said.
19) Thumb any dive that is not right. Better to live to dive another day. Don't get pressured to go or do something you are not trained for or are not comfortable with.
20) Write and submit a trip report to ScubaBoard when you return.
Wristshot
