Learn Spanish
The most important preparation would be to learn Spanish, because it will open the way to the people and culture. You can search the web and chose from the large number of schools available with different styles of instruction. You can usually make your arrangements over the internet, though calling and talking to the school can be helpful in judging their competence and making sure that they understand your needs. I would seriously suggest that you consider schools outside of Mexico City if you can. They tend to be cheaper and the cities or towns are better places to interact with Mexican people and culture. Also the general cost of living with a Mexican family or on your own will be less. Personally, I would avoid beach resort schools, schools in very large cities (Mexico City and Guadalajara) and a few towns with an excess of tourists and schools (Cuernavaca, Guanajuato, and maybe San...
