There is nothing more repulsive and foolish than cheating in a game of Magic, so simply don't get caught. The easiest time to cheat is when you are playing a multiplayer game, where people are farther apart. You have to be fairly slick to pull of a cheat in a one on one game, because the other player has nothing else to do besides watching your turn.
When about to cheat do not give off a repeated signal, instead try to stay in the background and don't let the people see you. You can try to cheat at the following times: Overlap cards (Put the top 2 cards of you library at the bottom instead of one), while the other person is reading their cards, when the other person is calculating, changing your attack powers (make something up), and a good old fashion knocking your deck over so you can reshuffle, and change cards.
When cheating, be fast. Don't sit there and play around and think. You must do it fast and before anyone notices. Also don't cheat at the beggining of the game. You should try this later in the game when the other player can't catch up with you. When cheating, try some simple magic (Like setting 2 cards on the top of your deck, but not shuffling them into the rest).
Newbies have tonnes of mistakes in Magic the gathering, and most experienced players will let such things slide. So act like a newb. It is that simple. For example: (Draw extra cards, only tap 2 land for a 3 mana creature). Only do this while having lots of land. You can also try pulling stunts like: Using the wrong type of mana to play creatures and spells, acting completely dumb (while have a specific strategy that will benefit from this), and taking a mulligan while drawing the same amount of cards.
Remember cheaters aren�t allowed in tournaments, at least the cheaters who get caught.