How to get good at BMX?

I love BMX biking but, I'm not very good. I really want to get better but my towns skate park only has a couple small ramps and some crappy rails. and there really isnt any where else to go. How can i get better. the only tricks I can do are Spine transfer and Hip transfer. i would love to learn to do a barspin or something in the air. but im afraid the ramps arent wide enough and i will go flying into the steel fence that is conveniently placed right next to the main ramp.