I had my first by caesarian in 2011 and 3 years later had my second by vbac. Now I'm 18 weeks with #3 and planning for another vbac. I didn't really do anything special to prepare, it just worked well naturally. My doctor was really supportive of trying a vbac and i think that helped alot. That was one thing people told me last time, was that if your doctor isn't really supportive of it, it can be harder to be successful. Good luck!
I don't think you need to do anything to prepare. This is all pretty natural and instinctual stuff. Lots of women do have VBAC. My sister did. Her first baby was breech and they couldn't turn her. She had her next two vaginally. No issues at all. good luck hon