The first day that I made my book free for 24 hours, I didn't advertise it on any sites. Actually, I didn't know of any sites that advertised Kindle free books. Turns out there are lots of sites but I will get to that later.
Prior to the promotion I was only selling a few books per week, mostly on the week days. So I decided to do the promotion on a Sunday. Low and behold, I had over 300 downloads that day. Tristan was right. My downloads increased over 600% in one day. Unfortunately, I didn't see an increase in sales after the promotion. Sales were still a few per week.
Next I saw a post on Marketing Easy Street. http://marketingeasystreet.com/how-to-launch-book.php. I decided to try the free promotion again and I listed my promotion on the sites listed in the article. Bingo!
The first hour of the promotion I had passed the number of downloads that I got in one day before. By the afternoon, my downloads were in the thousands and by evening, my book had reached No. 1 in Free Teen Science Fiction and No. 2 in Free Teen Paranormal. WooHoo!
In addition, after the free promotion was over my paid sales increased.
I am no longer in Kindle Select because I want my book to be available in all formats. However, I do agree that it is a great way to launch a book.
I would love to hear your experiences in the comments.