As follows is trouble_fish's take on mind tricks:
The use of psychological "warfare" is a standard tactic in any game. You use tactics that make your opponent do things advantageous to yourself. You do this by following tactics, gestures, and talk that does not reveal your true intentions, but rather what you want your opponent to believe. Your opponents may make assumptions about you, but it is your job to break those assumptions and continue to surprise your opponent.
To start, find out from your friends if you have picked up a habit like fiddling with a card you may play during someone else's turn or looking at a card in play you might destroy. Be aware of the habit, but pretend to continue it in ways that do not really show you're intentions. For example, handle a card in your hand that's not the appropriate spell or even appropriate for the situation. You opponent may think you have a trick up your sleve, but really the card is a useless island.
You must constantly show that you can either do more or do less than you actually can do. If you show exactly what you can do, you will never be able to decieve your opponent. If you do not show exactly what you can do, perhaps, sometime in the future, you can actually do what you showed. You will be flexible.
Always be on the alert of how to use your opponent's cards against him. Cards that affect all players like Warped Devotion and Dream Halls can be used for your own benefit even if your opponent plays one of those cards. Be prepared to be surprised by your opponent and adapt your strategy, not just your cards, to each deck you play against. Check for weaknesses in the opposing deck(s), and concentrate on being prepared to exploit them. If an opponent's deck can't deal with flying, perhaps it is not the best idea to put in more flying creatures, but rather concentrate on protecting the ones you already have. Then, check for weaknesses in your own deck. A smart opponent will be using the same tricks, and will also exploit your weaknesses in their choice of cards. Be prepared.
Also, continue to think of new ways to use cards. Be as creative as you possibly can. For example, Shelter is usually used to protect your creature from damage. But it can also be used to make your creature unblockable, to counter an enemy spell targeting either your or their creature, to remove enchantments from any creature, or simply to draw a card. There are hundreds of cards with multiple uses or cards that haven't been "discovered" yet.
In single player, press yourself to kill the opponent and win the game mercilessly. Attack at every good opportunity. Deal as much damage as you can. Don't be forced on the defensive. Your deck should have cards to break stalemates. Constantly be calculating. Magic is about math. Basically, any method to reduce that 20 life to zero will do.
Finally, when the opportunity suits, throw out all this strategy and plotting and go for broke. This can take people completely by surprise. I have wasted opponents because I went all out and hid nothing.
To sum up, do things you are not expected to do. Hide all your intentions and mislead your opponent, subtly. Find weaknesses in your opponents and yourself. Be creative with our cards and act to kill the enemy. Be calculating, extracting the most damage possible. And be spontaneous, to throw your opponent off at the perfect moment. With all this thinking on your side, how can you lose?...
um... dumb question... you will be anniahlated by me of course!
MUHAHAHAHAHAHA!