How to make friends in Mexico

Depends upon whether you  are interested in meeting Mexicans or Gringos.  Best way to meet Mexicans is to study Spanish so that you can communicate, and then use it at every opportunity. Mexicans  are very forgiving of our mistakes and pleased when  we try. Or you can stay in a place where English is widely spoken and try to connect that way.

Best way to meet anyone anywhere is to be open, willing to make the first step, interested in what others do and think.  In the expat communities around Mexico (Lake Chapala, San MIguel Allende, etc.) there are various expat volunteer organizations such as art societies, photographic and computer clubs, etc. Join as many as you have time and interest in.  Ask questions, reach out to others.  Particularly good for meeting both Mexicans and Gringos is to join gringo organizations that support local charities such as food banks, battered women, orphanages, etc.  They are desperate for the help the response is very warm and welcoming.

Good luck!