It depends where you want to teach... unfortunately, it is very hard to get a visa in Japan if you don't have a B.A. (or 3 years relevant experience in the field). If you don't have the B.A., you have to come in on a cultural visa or student visa, both of which limit the amount of hours you are allowed to work.
Since you don't have a B.A., a TESL course would be good for you. Oxford seminars have automatic placement, but you can't choose your location- you might end up in Africa or Romania or Chile! If it doesn't matter to you where you are, then they might be a good route.
Another thing I would really suggest you do is start making a portfolio of work in something related to what you want to do. This will help employers see how valuable you will be to their company