And this goes without saying: ditch the tourist/resort areas and scout out the more traditional areas surrounding the city. I haven't been to Cancun, but this applies to just about any destination in Mexico. You'll encounter more interesting people (as opposed to Spring Breakers or old folks in black socks) and everything will be cheaper.
__________________ ¿Donde esta Omid? Omi-san wa doko desuka? Ou est Omid? Wo ist Omid?