Check the listings for TESOL courses in your area. Websites such as ESL Gold offer listings of courses in California.
Examine university courses. These programs usually have the best reputation, but are sometimes more expensive and run for a longer time than smaller private schools.
Check smaller private schools in your area. These are often the cheapest option, but be careful. Most courses are legitimate, but some are scams that fail to provide an internationally recognized TESOL certificate. Visit the TESOL website (tesol.org) and send an e-mail inquiry if you are unsure.
Make a list of the courses that interest you and compare them. Consider price, duration and the quality of the program. Email some of the programs and ask for application packages if they aren't provided on the program website.
Enroll in the class that interests you the most. For university programs, you may have to apply several months in advance. Some smaller private schools admit students year round.