Peter Anspach posted this list. Here are some of my favorites.

1. My Legions of Terror will have helmets with clear plexiglass visors, not face-concealing ones.
2. My ventilation ducts will be too small to crawl through.
3. My noble half-brother whose throne I usurped will be killed, not kept anonymously imprisoned in a forgotten cell of my dungeon.
4. Shooting is not too good for my enemies.
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 Dragons of Eternity. It will be in my safe-deposit box. The same applies to the object which is my one weakness.
6. I will not gloat over my enemies’ predicament before killing them.
7. When I’ve captured my adversary and he says, “Look, before you kill me, will you at least tell me what this is all about?” I’ll say, “No.” and shoot him. No, on second thought I’ll shoot him then say “No.”
8. After I kidnap the beautiful princess, we will be married immediately in a quiet civil ceremony, not a lavish spectacle in three weeks’ time during which the final phase of my plan will be carried out.
9. I will not include a self-destruct mechanism unless absolutely necessary. If it is necessary, it will not be a large red button labelled “Danger: Do Not Push”. The big red button marked “Do Not Push” will instead trigger a spray of bullets on anyone stupid enough to disregard it. Similarly, the ON/OFF switch will not clearly be labelled as such.
10. I will not interrogate my enemies in the inner sanctum — a small hotel well outside my borders will work just as well.
11. I will be secure in my superiority. Therefore, I will feel no need to prove it by leaving clues in the form of riddles or leaving my weaker enemies alive to show they pose no threat.
12. One of my advisors will be an average five-year-old child. Any flaws in my plan that he is able to spot will be corrected before implementation.

via Peter’s Evil Overlord List.