When you start performing, engage the audience. As part of your patter, ask them some questions and start a conversation. Have a couple of lines of dialog in your script before you start doing anything with your hands.
What the heck am I talking about? Nerves are a result of two things... a fear of looking foolish and a fear of the audience not being interested. By talking to your audience you get them interested. You also get positive feedback by asking them questions. Your brain is tricked into thinking that this is a regular conversation -- something you have done millions of times.
Also, make sure you rehearse your presentation. That is, have a script and learn it the same way you learn the sleights. Then practice speaking the words while you do the sleights. When you start to perform it will feel just like practice as soon as you say the first sentence and you will be less nervous.