I would say also try to get to know the Mexican locals. Since Cancun is a very young city (40 years), pretty much everyone who lives here is from another city or state, not just the expats. I've been here 5 years and didn't make any native English-speaking friends until 6 months ago. My best friendships here are almost entirely with Mexicans, and it's been invaluable in understanding the culture and helping me get over culture shock. The openmindedness of the Cancunenses has allowed me to ask them so many questions. So long as I'm gracious and nonjudgemental, everyone has been so helpful. The street called Yaxchilan is a great place to meet people your age on weekends. (La Taberna is located there). Just make sure to stay away from the bars with tinted windows. They tend to be sketchy. La Taberna, 77, El Asador and La Parrilla are great bars on this street. My absolute favorite is Los Arcos.
My favorite is Los Arcos too. My friends boyfriend plays with a band there sometimes. And the food and 2X1 beers are a big bonus.
I live on Av La Costa downtown and always up for meeting new people, I live with 6 other English Entertainers too, we get Thursday and Sundays off.