Because what one shouldn't do is just as important as what should do. Put up tips on how to be a bad GM. I'll start.
1.Railroad Plot, plan out every major event in advance, if your players somehow manage to worm their way out of the delightfully contrived story you've crafted then deus ex machina them back into it, use dragons if you have to.
2.Make the characters obsolete. So your characters have gotten that super-awesome ability they've been looking forward to since the games start? Crap, you havn't thought about how to deal with it, it could ruin your beautifully crafted plot! Quick! instead of figuring out an idea to make it work rewrite the script so that your players continually get thrown into situations where that snazzy new teleportation spell is useless.
3. Have your characters overshadowed by npc's, your players arn't humble enough, it's time to show them how little they matter in the scheme of your plot. Add an awesome npc to the group, have them be far stronger than any of your characters in that characters area of specialisation. Let this npc be batman to your parties robin. Contrive events where he needs to save your players from certain doom, let him narrarate plot constantly instead of letting the players figure out what's going on for themselves, have the npc take down dragons and main villians right in front of the main characters, while they stand helpless to really do anything. After all, your npc is the major plot driving force, your players are just along for the ride right?