This is not to say you can't get a job, or you must have an IQ like Einstein. The truth is, teaching English at a conversation school is more entertaining than educating. And if you are a young, single woman, you have an automatic advantage. In fact, going to the job interview in a tight suit and high heels might just double your chances. In any case, a positive attitude, an outgoing personality, and having a lot of interesting stories to tell are all important factors.
Personal contact is very important in Japan.
Nearly all schools run on a one-year contract system. Afterwards if you renew your visa, you can get up to a 3 year visa. The Japanese school year starts in April and hiring season is usually January through March. If you miss this critical window, getting a job will be that much harder. Either they scored in getting a new influx of students, or they hired and fired an incompetent teacher, a teacher decided to call it quits, or they treat their teachers like used toilet paper and they're looking for a new sucker.