Attitude

One thing people frequently do is to have a very silly attitude at the poker table.  First of all, never yell at anyone for making mistakes, and don't tell them how they're playing wrong.  When you have AA and you raise it up, and someone calls you with an 83o or some such junk, and they wind up beating you, it's natural to feel a little mad.  Don't.  Be happy - they're playing badly, and they're going to pay you in the long term.  You should do what you can to keep them in the game, to keep playing with them so that you can take that money back.  If you curse at them and chase them away you can't win that money back.  Obviously you shouldn't be lecturing people on how to play better - you don't want them to get better, and you don't want them to know that you read a lot of books and think about poker theory and things like that.  (Note that all of these guidelines may be broken when you are intentionally play-acting to create some sort of image or trying to get your opponent to react in some way or other).  Also beware that your opponent may not actually be playing badly.  When you take a bad beat, you can lose your mind a bit, and you may not realize that they actually were playing well.  Yes, perhaps they drew out on you, but maybe they actually had good implied odds, so calling your bet was a good play.  Make sure you are aware of the situation that they were in when they made those plays before deciding they're just a bad player.