I'm sure you've heard "when in Rome.... do as the Romans do," but when stepping into a foreign country it's really worth considering these words a bit more carefully. The saying originated in 387 A.D. when St. Augustine arrived in Milan and observed the Catholic Church did not fast on Saturday like it was done in Rome. He consulted the Bishop of Milan (St. Ambrose) about the matter who simply replied: "When I am in Rome I fast on Saturday; when I am in Milan, I do not. Follow the custom of where you are." That sentiment has stood the test of time and can really make a difference when visiting Mexico , or any other country for that matter.
I have traveled the world and feel there is nothing more frustrating than watching "ugly Americans" (Canadians are guilty, too!) being rude or disrespectful to the local people. Regardless of whether it's an all-inclusive in Cancun where everyone speaks English, or an eco-hotel in the remote jungle of Chiapas, you are still a guest in Mexico... you are still visiting someone's home. As a citizen of the world, you owe it to yourself and your hosts to take the time to understand the basics of the Mexican culture and to embrace their hospitality with the respect it deserves. I have seen bad manners exhibited many times in Mexico, so I am hoping to shed a little light on some common courtesies that may change your travel experience. At the very least, it will bring a smile to your Mexican hosts!
First, let's talk about changing your mindset when you plan a trip to Mexico and switch from being a tourist to being a traveler. What's the difference? Plenty...
• A tourist expects (and insists) everyone speaks English. A traveler tries to use even the most basic high school Spanish to make an effort.
• A tourist is content to hang out at the swim-up bar getting lobster-red sunburn while becoming louder, drunker, and more obnoxious by the minute. The traveler heads into town, checks out the local markets, tries to make heads or tails of the menus at local restaurants and takes the time to stroll the streets, smile at the people and take in the flavor and color of the place they are visiting.
• A tourist goes to the local McDonalds, American chain restaurant, or orders a hamburger at the hotel. A traveler will find out where the best local dishes are served and at the very least give them a try.
• A tourist is content to be part of a group and to take large tours to all the most famous spots. A traveler tends to rent a car with a few other people (or solo) and explore the area on their own.
That list could go on forever, but you get the idea.
Mexico is also far more formal than many would think. If you know anything about Mexican history, you know the Spanish had a tremendous influence on the people and culture of the country. The early Spanish overlords who came to Mexico  in the 1500s brought the etiquette of the Royal Court of Spain, and many of those formalities still exist. As a rule, the Mexicans have maintained this cortesía, and it's important that foreigners be aware and sensitive to not insulting the dignidad of the people they encounter.
• For starters, it helps to use Señor (Mr.) or Señora (Mrs.) with the men or women you encounter. Mexicans always address by social status and this immediately shows respect and will be a quick step in the right direction. (Señorita would be used to address a young, unmarried woman and is similar to Miss.)
• In a restaurant, if you wish to call the waiter, you generally use the term Joven (Ho-ven). Though it means "young person," it is an accepted term for all waiters. If you have a waitress, Señorita is appropriate. Snapping your fingers? Never.
• "Please" (por favor) and "Thank You" (gracias) are a given if you'd like to ask an employee (or anyone for that matter) to do something. Look them in the eye and be sincere, it will take you a long way.
• Americans tend to enter a room of strangers and only say hello in passing, if at all. They are usually casual, self absorbed and miss the almost constant greetings by their Mexican counterparts. Whether it's in a public place with strangers, or with people you already know, say buenos días (good morning), buenas tardes (good afternoon) or buenas noches (good evening) to those you see. You'll notice smiles right away.
• Being humble is a cultural virtue often forgotten by visitors. Mexicans will always welcome you when you arrive to your destination and refer to their home or even your hotel as su casa (your house). They are modest and truly want you to feel at home in their country. Keep an eye out for that and be sure to thank them for their hospitality.
• If you can't speak Spanish, don't insult the local people by shouting louder and slower in English. It's rude and it doesn't change the fact that they don't understand. They will appreciate any effort you make, regardless of your skill level.
• YES it is customary to tip in Mexico. Here is a great article for reference: http://gomexico.about.com/od/historyculture/qt/tipping_in_mexico.htm 
• Come to a church just as you would at home. Be aware when entering and always take off sunglasses, baseball caps or hats. Wearing shorts is rarely an issue in the beach areas, but women should take care to wear a wrap or sweater to the waist to avoid showing too much skin, which could viewed disrespectful in such places.
• The beach is the beach, but away from the resort areas shorts are very rarely worn by Mexicans on the street. Be cognizant of how you look and avoid drawing too much attention to yourself as a foreigner. Never wear shorts to a business event or to a restaurant outside the immediate resort area.
The Mexican culture isn't overly complex. It's built on simplicity, humility and courtesy. The people are tremendously warm and inviting, and genuinely care about their guests. Whether you're a tourist, a traveler, or a little of both, take an extra few minutes to embrace Mexico at its core and I think you'll come away with a deeper appreciation of a country waiting to invite you home.