avoid cancun like the plague. we spent a few days in playa del carmen and that had quite enough touristy shite for us, thankyouverymuch. it erred on the side of still being lovely - i've heard rubbish things about cancun. if you want to see the ruins near the very touristy areas go in the very early morning or last thing at night. i highly recommend the ruins at Palenque - go for when gates open, get yerself a guide and listen to the howler monkeys

don't stay past about 10am though, cos it's in the middle of the jungle and is seriously humid.
tipping is part and parcel of almost all bars & restaurants - the prices reflect this though. allow for the fact that mexican service is very laid back and don't expect all your meals to come at the same time. beer is cheap. so is tequila.
when visiting native mayan villages don't take photos unless EXPRESSLY told that you can.
don't give money to child beggars, no matter how much it breaks your heart - if you give them money it gives them a reason to be out on the streets and travellers are encouraged not to give out cash for this reason. Some areas around the Yutacan peninsula got hit really hard by strikes and political unrest a few years back - wiped out the local economy (almost all tourism) and although they've made great strides in gettign back on their feet there are still huge numbers of folk who are desperately poor.
the bus service is far superior to anything you'll find in the UK. pretty cheap and mostly comfortable. best way to get about between cities. you can fly too but go overnight on a coach and save yourself a night's accommodation.
it takes ages to find the @ symbol on a spanish-set keyboard.
DO learn some spanish (if you don't speak it already). Latin American spanish doesn't have the 'th' sound so is often a bit easier.
crafts - tin, day of the dead stuff, textiles (good haggling to be had), silver (also good haggling to be had), also coffee and chocolate. and fried grasshoppers. (ask connor o'bain)
everything comes with cottage cheese, guacamole, and refried beans.
you will probably get a bout of montezuma's revenge. bring rehydration salts.
take millions and millions of photos
