I'm still learning some of this stuff, but I think giving away a few of your books on goodreads.com can lead to increased sales. I know that it certainly helped increase my visibility. I gave away five copies of my latest book, The Curtain Torn, and I had almost 600 people sign up for the drawing. I can't track how many additional ebooks I sold due to that, but I think it's worth it. Also, even though they say it's for books less than six months old, the published date is optional, so you should be able to give away previously published books.