Current uni student, what should I do to prepare to work as a teacher in Japan?

I am currently a student at university, studying English Language and Japanese and I really want to teach English in Japan after receiving my degree.

After getting my degree, I’m thinking of going to a language school in Japan to learn even more Japanese. I also want to become an English teacher in Japan after that.

My question is, what should I do before I start looking for English teaching jobs in the future? Should I get a TESOL certificate, take the JLPT, get any work experience or get any other teaching qualifications from my own country (UK). Would any of these increase my chances of getting a job in the future?

Thanks in advance