Predictability

[@@] Varying your play.  Playing solidly and well but predictably is very bad.  Make the same plays with very different cards.  Your opponent only sees your plays, don't let him predict your cards from your plays.

[@@] Common mistakes - telegraphing overcards, telegraphing middle or top pair, telegraphing pocket pairs, too consistently slow-playing your monsters.

A big advantage of being constantly aggressive is that people don't know if you are bluffing or have a monster.  This makes them afraid to call your bluffs, and it makes them pay off your monsters.

Playing strangely is an advantage in that it throws off your opponents.  However, it is in itself a losing proposition.  For example, playing bad hole cards will confuse your opponents, but they will win so rarely that you are losing money on average by making that play.  In fact, that's almost the definition of "playing strangely" - your opponents can't put you on your cards because you're playing them wrong, in a way that loses money on average.  The trick is to make these plays and lose only a little bit of money, by playing small pots strangely, and playing big pots well.  For example, in a No Limit tournament, you might frequently limp with very bad hole cards.  This is a very cheap play, and if your opponents let you do it (by not raising), you should.  Now, you may win some hands this way if you hit good flops, or you may bluff out your opponent and show them the junk cards.  Once you've done this, you've set them up so that you can win some very bit pots when you're playing good hands.  The key to remember with all this is that you're still playing for +EV in the long term, playing wildly is not a positive thing on its own.