Sightseeing
Short shorts and scant tops are not acceptable in churches, despite the fact that shorts are. While attending church, avoid taking in the sights, however you can observe from the rear. Otherwise, taking pictures is not a problem. If photography or flash photography is prohibited, there is typically a sign at the front of the church. It is customary to offer elderly or disabled people who are begging at church entrances a few coins.
Say "con permiso" (excuse me) to move past a group of people. It is customary politeness to give up one's seat on a bus to the elderly, the blind, and expectant women. No matter their age, Mexicans refer to waiters as joven (literally, young man). Say "seorita" (miss) or "seora" (ma'am) when addressing a female waiter. When you want the bill, ask for "la cuenta, por favor" (the check, please); it's typically viewed as impolite for a server to provide it before a customer requests it.
For a night out, Mexicans typically dress properly, but in tourist areas, dress codes are typically only observed at the more upscale discotheques. While some restaurants have designated smoking areas, you can normally smoke in smaller places.