Inspired by Peter's Evil Overlord list - a list of dos and don'ts for evil overlords based on classic mistakes by such. I'm only writing down a few things that have been really bugging me, mostly Marik and Bakura centered, so feel free to add anything that's been annoying you in your comments! Just follow the format you see in the ones I write.
#1: If I have two of my nemesis' best friends mind controlled, I'll have one of them get him alone and stab him. I will not make one challenge him to a children's card game.
#2: If my nemesis seems really anxious for me to do something that I think will further my plot, I will stop and re-examine the situation before proceeding. They probably don't have my best interests at heart.
#3: If a fake card I've created has fried the brains of at least 50% of the people who used it, I will not make my beloved foster brother use it.
#4: Forget that. Just don't have a foster brother in the first place. Nothing but trouble.
#5: If my goody-two-shoes host is controlling my left hand at a critical juncture, I will not blithely assume that things will be fine if I move the computer out of my left hand's reach. I will excuse myself from the table momentarily for some duct tape and secure said hand to the table, preventing any annoyances.
#6: If I have an alter ego that wants to kill me, I will visit a competent psychiatrist. The heroes will have no excuse to help me out, and I won't have to ally with them.
#7: If my nemesis is less than five feet tall, I stand at least a head and a half taller than him, and he is extremely shrimpy from doing nothing but play card games all day long whereas I actually have some muscles, I will not conduct long and elaborate plans to beat him through card games. I will punch him in the face and take his puzzle because there's not a friggin' thing he can do about it.
#8: I will not promise my unstable ally my
super-special-awesome family heirloom rod that controls minds, because this is something I'll probably end up regretting. I will instead offer him my sister, who is worth less to my evil plan. He's gotta be lonely after 3000 years in a ring.
#9: I will do something about the hair and eyes changes that occur when I take over from my host. Maybe contacts and hair gel. Nobody's noticed yet, but you never know, I could meet someone with eyesight.
#10: If I'm about to kill/interrogate someone and I'm called, I'll just say 'Be there in a minute' and finish up. Punctuality is not that important.
So, there's my 10 cents. Please feel free to contribute more!