Some helpful hints can be found here
Peter's Evil Overlord List
A few examples:
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.
The hero is not entitled to a last kiss, a last cigarette, or any other form of last request.
I will never employ any device with a digital countdown. If I find that such a device is absolutely unavoidable, I will set it to activate when the counter reaches 117 and the hero is just putting his plan into operation.
I will never utter the sentence "But before I kill you, there's just one thing I want to know."
When I employ people as advisors, I will occasionally listen to their advice.
Despite its proven stress-relieving effect, I will not indulge in maniacal laughter. When so occupied, it's too easy to miss unexpected developments that a more attentive individual could adjust to accordingly.
I will hire a talented fashion designer to create original uniforms for my Legions of Terror, as opposed to some cheap knock-offs that make them look like Nazi stormtroopers, Roman footsoldiers, or savage Mongol hordes. All were eventually defeated and I want my troops to have a more positive mind-set.
No matter how tempted I am with the prospect of unlimited power, I will not consume any energy field bigger than my head.
I will keep a special cache of low-tech weapons and train my troops in their use. That way -- even if the heroes manage to neutralize my power generator and/or render the standard-issue energy weapons useless -- my troops will not be overrun by a handful of savages armed with spears and rocks.
I will maintain a realistic assessment of my strengths and weaknesses. Even though this takes some of the fun out of the job, at least I will never utter the line "No, this cannot be! I AM INVINCIBLE!!!" (After that, death is usually instantaneous.)
No matter how well it would perform, I will never construct any sort of machinery which is completely indestructible except for one small and virtually inaccessible vulnerable spot.