I applied to the JET Programme twice a few years ago and didn't get on, it's crazy competitive. If you do get on, it's a great experience. I ended up going out to Japan with a private company, I've recently come back to pursue a PGCE. Many of my friends out there were JETs. JET is well known for being the best paid teaching gig in Japan for a foreigner but it's a bit pot luck as to whether you get a good placement or not. PM me if you want to know more about what to expect working in Japan or about alternatives to JET.