One-day Sales and Social Networking

Have any of you other craft sellers ever had a one-day sale on Etsy or any other site? I'm planning on having one for my shop but I don't know what to expect.

I've never done one before, and just wanted to know if any of you have and if you might be able to give me some tips?

Also, if you use Twitter or Facebook for promoting your own shop, how much does it seem to help? I haven't had too terribly much luck with having a page on Facebook, and I've spent hours on Twitter trying to get more followers but not much seems to work. =/