A recent tips of the trade trick about e-mail had some great advice. I already do half of it, and plan to begin doing the other half.
The first part is to attach whatever you’re going to attach before you write the e-mail to avoid sending out the second e-mail explaining that you forgot to include the attachment. Whenever I mention an attachment, I attach the file to avoid that problem.
The second suggestion is to leave the to fields blank until you’re ready to send the e-mail. That’s a great idea, because not only does it keep you from sending a partially completed e-mail by mistake, it’s easier to decide who should receive the e-mail after you’ve written it.