1. Don't expect "Mexican Food"!
If you're a fan of Mexican food back home in the U.S. don't expect it to be the same in Mexico.
Mexican food in the U.S. is TexMex, a Texan/Mexican watered-down version of Mexican food made to be more favorable to the American palette.
You won't get Burritos, hard shell tacos, ground beef toppings, orange cheddar cheese, chimichangas, or a big bowl of nachos in Mexico!
Instead, you can expect Tacos, Tortas, Pozole, Tamales, and Enchiladas, with a wide range of exotic and spicey flavors, be careful with the spice though! things may be somewhat hotter than you expect.

2. Don't Bring Your Own Car.
If you have a car accident in Mexico, your American car insurance isn't valid.
If the accident is deemed to be your fault and you don't have Mexican car insurance, the police can detain you until you can prove that you can pay for the repairs.
So unless you want to buy Mexican car insurance or hire a car you're probably better off just using public transport.

3. Don't Hail a Taxi.
Not every cab in Mexico is licensed and a lot of the unlicensed cabs are involved in scams, extortion, and even kidnapping.
One of the methods is to pick up the client and instead of taking them to their destination, they take them to an ATM. They are then forced to take out money and had over their valuables and are then dropped off in some remote (and sometimes dangerous) neighborhood on the outskirts of the city.
If you need a taxi, use a "Taxi Rank" cab that you have to phone beforehand to book.

4. Don't Insult La Virgen De Guadalupe.
The Virgen of Guadalupe is Mexico's patron saint and an important religious symbol.
In 2002, Pope John Paul II declared her the patroness of the Americas, and her birthday, which is on the 12th of December is a national holiday.
Even if you are not religious, you should treat Guadalupe with respect because insulting her is like telling someone from North Carolina that Nascar is boring and America sucks.

5. Don't Be Brash With Your Cash.
It is never a good idea to go around with a huge wad of cash on you or flashing your valuables, it is always best to carry a smaller amount, or separate a larger wad and stow it in different locations.
In Mexico, it's also a good idea to be careful with your cards.
Avoid using debit cards at gas stations because of card skimming, and never give your card to a server at a restaurant, instead, make sure to pay at their card terminal.

6. Don't Expect Them to Hablar Ingles!
In general, we English speakers expect foreigners to speak our language.
If we go to Sweden, we expect them to speak English, however, the idea of a Swede coming to America and expecting us to speak Swedish seems preposterous!
In Mexico, the native tongue is Spanish, and although many people there may speak and understand a little English, it is always more respectful and better received by the locals, that the visitor should, at least attempt to speak their language.

7. Don't Wear Flip-Flops.
Flip-Flops are for the beach and shouldn't really be worn anywhere else! this is not just because of that annoying "Kerplick, Kerplock" sound they make but also because they instantly announce that you are a tourist and that they are impractical and unhygienic, especially if you are in a city.
Cities are dirty places and you tend to walk a lot more than you think when visiting one, so to avoid having blisters and skanky feet at the end of the day get yourself a pair of closed sandals or comfortable sneakers.

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