you look at your hands while practicing, you will form the habit of looking at them — a habit which you cannot have if you are to be a real Magician. So train yourself right from the beginning not to watch your hands. Each day when you practice, pretend you are before your audience. This will make you do your moves in the best possible manner.

BE SURE OF YOUR TRICK

You must expect to find someone in every audience who will try to belittle your ability as an entertainer and magician. If you are not sure of yourself, such a person can make your performance a farce. He may expose your secrets and make you a failure as a Magician. Let no move of any trick remain unmastered. The less mystery there is to you in a trick -- the more mystery it will have for the audience. BE SURE THAT YOU CAN DO YOUR TRICK before demonstrating it. With practice will come self confidence, ease of performance, and unquestionable ability to put it across.

NEVER REPEAT A TRICK AT SAME PERFORMANCE

Something you must adhere to absolutely is never to perform the same trick twice to the same audience during the same performance. When you have them mystified, leave them mystified. Don't lift the illusion. Don't break your effect by repeating the trick. What your audience has missed the first time, they will watch for the second time, and so may discover your secret. And then, of course, you have lost your hold on them. So remember, never repeat the same trick by the same method during the same performance.
Harlan Tarbell was the mentor of many gnerations of magicians through his famous correspondance course The Original Tarbell Course In Magic