ESL opportunities in the U.S. are mainly found in Community Colleges and Universities. To teach at a College or University you would need to be fairly well qualified - an MA is often listed among the job requirements. What qualification do you already have, and are you a US citizen and a native English speaker? These are the things most employers will be looking at. You might be interested in the article on teaching in the USA published in the ICALWiki at www.icalweb.com/wiki