I'm going to Cancun. What should I do there?

Have your picture taken with a donkey.

Eat a lot of tacos

There are so many things to do and see in the area that you won't be able to do it all in one vacation. My wife and I have been vacationing in the Maya Riviera each year for several years now, and we still have plenty of new places to visit. If you will be staying in a resort, they will have a tour desk that you can book your excursions. Be careful of anyone approaching you with discount tours at the airport. Take some eco friendly sun screen with you just in case you decide to check out some of the theme parks. They won't let you in with regular sun screen. As for the safety aspect, don't flash your money around, and don't get falling down drunk.  

watch out for the drug cartels

Robert has clearly never been to Cancun. Cancun is mostly resorts, and it's all about the beach, the pools and the bars. It's not like real towns in Mexico. But it's perfectly safe. The one thing you can do is book a day trip to Chichen Itza. We did that the last time we were there, and it was very interesting. 

I have a business in Mexico. I'm there 30 times a year...no kidding. Don't let these people scare you. Certainly, you want to be cautious whenever you travel anywhere. Don't drink the water....for sure don't drink the water. I don't even brush my teeth with it. Don't go to night clubs at night alone. Negotiate with the vendors. Walk away and they will lower the price....usually 2 or 3 times. Eat food that you normally wouldn't eat....you're on vacation. Try different foods. Think carefully before you buy a souvenir. Are you really going to use this thing? Relax, enjoy, repeat. 

Use plenty of sunscreen and don't buy any weed from kids trying to sell it to you either on the beach or on the street!

Watch out for terrorists, drug addicts, and don't drink the water or the dangerous liquor.

Don't leave the guarded compound of the resort where you are staying. Don't leave your room without someone with you. Stay withing sight of the security cameras at all time. Don't talk to strangers or any staff member trying to separate you from your friends. Other than that have a fun time.