Having your material down pat will greatly help. It is one less thing to thing about and worry about.
Also, don't worry about screwing up. It will happen. Eventually, something will go wrong. Just accept it, learn from it, and go on. I remember a few years ago, when I was performing the toss out deck, the rubber band came off the deck and cards exploded everywhere. It sucked. But it wasn't the end of the world. Now, I use three rubber bands on my deck, and it has never happened again. However, I know that there will be other problems in the future.
Then as Paddy first said, just do it. Get as many performances under your belt as you can while maintaining a professional show. The more you do it, the more comfortable you will get. It may not make all of your anxiety go away, but it will greatly help.