Pre-announced and got people to sign up to my mailing list in return they got chapter 1 and the table of contents early. I write a weekly email about side projects and building products so a lot of my early traffic came from that. We did exactly the same thing when we launched Perch, and that launch day paid back in sales everything we had spent on the product to get it to launch (not our time but actual cash outlay).

You need to be building an audience for your book long before you actually launch it if you want to have a decent launch. Nathan Barry writes some good stuff about this, check out his book Authority: http://nathanbarry.com/authority/