Be professional: You don't want someone to not buy what you're doing. You're trying to create an illusion. You're trying to be believable.
Be calm: look like you belong there.
Know your mark: Know your enemy. Know exactly how they will react before they do.
Do not fool a superior scammer: Trying to outscam an observant or smarter person will end in disaster.
Plan your escape from your scam: Lets say someone is suspicious. Don't burn your bridges and walk away. Save the source.
Try to be a woman: It's proven that women are more trusted over the phone. Use that to an advantage. Get a woman's help if needed. It's even better if you're actually a woman (a rareity in our biz).
Watermarks: Learn to make 'em. They are invaluable for a mail scam.
Business cards and fake names: Use them for professional things.
Manipulate the less fortunate and the stupid
Use a team if you have to: Don't be arrogant and overly proud. If you need help, get it