Thurston's three rules of magic are STILL the rules that professional and hobby magicians go by as their "code of conduct" and they are:
Never reveal the secret to a trick—it ruins the mystery.
Do not repeat tricks in front of the same audience—no matter how much they beg! Most magic is based on the spectator not knowing what to expect. The second time around they will know what to look for, and might spot the secret!
Practice to Perfection – never show a trick until you can do it properly every time—A poorly done trick inadvertently breaks rule No. 1.