I taught English in Japan for two years. It's how most foreigners from English-speaking countries get their start here, so for those of you considering moving to Japan, I thought I'd share my thoughts with you.

Primary/Secondary Schools or English Conversation?

There are two primary entry-level English teacher jobs in Japan: positions at Japanese public and private primary and secondary schools, and positions at English conversation schools (英会話, eikaiwa).

The public/private schools have better benefits, are generally full time, and allow one to experience the Japanese school system and Japanese culture in a way that few other jobs allow. However, these jobs are hard to come by in the biggest cities. The English conversation schools are generally part time, but the salary is decent and you can generally find work even in the biggest cities.

Primary/Secondary Schools

For teaching primary and secondary school students, the best program is clearly JET. For those ineligible for JET, I recommend looking for a smaller program based on JET. There are several of these in Japan, but they are increasingly hard to find.