Training a thoroughbred horse?

I have just bought an ex-racehorse and am now beginning to start training it to jump. I am only trotting her at the present as i want her flatwork to be good first. Any tips on how to start training her to jump would be great. Also i don't have access to an arena until the summer but have very good fields to ride her in and they are dry and flat. Will this be ok? Thanks :)