As everyone else said, but also it's great to have a trainer. As experienced as you think you are, you never know what you could be doing wrong (I'm not trying to be rude - this goes for everyone in general). Once you and your horse have the basics down, it'll be so much easier. Do you have any jumping experience? Does your horse have any at all?
Start out small, get him/her used to poles, but take it slow. If he/she's great with a pole, don't put it up to a huge cross rail. Put it up to a tiny cross trail, and make sure he/she gets the picture to pick up his/her feet!
But a trainer is really the best way to go. Look into it!