Where's the Happy Medium?

I need to figure out the happy medium when first meeting someone. Where is the fine line between saying too much information and being too closed off? I never know how much is too much and obviously I've got diarrhea of the mouth and send people running for the hills. I wish I could be one of those mysterious people who never give out any information and leaves people wondering. Alas, I am the opposite of that. Perhaps I should just pass out a little information sheet and move the process along right at the start...that would save time, right? Or, just introduce as Pinky Lovejoy, certifiably insane. :)