Never be a failed Evil Overlord again. Make sure you read How to be a Successful Evil Overlord by Peter Anspach.
My favourite ones:
5. The artifact which is the source of my power will not be kept on the Mountain of Despair beyond the River of Fire guarded by the Dragon of Eternity. It will be in my safe-deposit box. The same applies to the object which is my one weakness.
56. My Legion of Terror will be trained in basic marksmanship. Any who cannot learn to hit a man-sized target at 10 meters will be used for target practice.
70. When my guards split up to search for intruders, they will always travel in groups of at least two. They will be trained so that if one of them disappears mysteriously while on patrol, the other will immediately initiate an alert and call for backup, instead of quizzically peering around a corner.
84. I will not have captives of one sex guarded by members of the opposite sex.
90. I will not design my main control room so that every workstation is facing away from the door.
Excerpt:
Being an Evil Overlord seems to be a good career choice. It pays well, there are all sorts of perks and you can set your own hours. However every Evil Overlord I've read about in books or seen in movies invariably gets overthrown and destroyed in the end. I've noticed that no matter whether they are barbarian lords, deranged wizards, mad scientists, or alien invaders, they always seem to make the same basic mistakes every single time.