One: avoid use of the word good to describe yourself or your mood. After all, 'well' is usually the grammatically correct term you are aiming for.
Two: have a lair. If you don't have a lair, just put up a sign outside the entrance to your parents' basement suite.
Three: keep said lair dimly lit. Squinting will add to your air of evilness.
Four: find a good narrator with a large vocabulary, because you will soon become tired of cackling maniacally.
Five: as tempting as it is, never reiterate your plans to the captured spy/secret agent/hero/etc.
Six: it is alright to have the heart of a little girl.*
Seven: have minions. A villain without minions is like Santa Claus without elves, but with less jolliness.
Eight: speak with an accent, even if you don't have an accent.**
Nine: attaching a laser to something doesn't always make it better. The same is true for jet propulsion engines.
Ten: always refer to things as your diabolical plan, whether it be to take over the diamond industry, bankrupt the leading nations of the world, or pick-up some apples from the grocery store on the way home from grandma's.
*in a jar on your desk.
**alternatively, take your evil villain business to a country where everyone else has an accent