When I applied I didn't get a place, they said partly because I didn't have relevant experience. I'd taught 16-18 year olds for a gcse equivalent qualification but not in a school setting. They said to get experience in a secondary setting and a relevant degree
When I was at university they ran a School Associate Scheme, Im not sure if they still run but if they do it could be a good way of gaining experience. Volunteering in school for a period of time each week would also strengthen your application.