I've taken to doing a "Billy Bobble Quote of the Week" that I boost for $5.
The boosting helps me reach younger readers. My fans are mostly in their 40s-50s because they came from my friends and Dances With Filmmakers. That's great for parents and grandparents, but if I want to reach teens, I need to target them. I also get to target based on other books, like Harry Potter, Ender's Game, etc.
For $5, my reach runs between 2K and 3K, with anywhere from 3-10 link clicks.
I'm right in the middle of a blog review tour, so I've been boosting posts with the reviews as well. Sometimes the links go to the blogger's site, so that's most likely not a sale, but I look at advertising as a way to raise awareness at this point. When book 2 is out, it won't have to break so much new ground.
That, and the reviews have all been fantastic, so maybe I'm just bragging. :)
From Elephant's Bookshelf Press
by R.S. Mellette
"WOW. That is the first word that comes to mind when I think about how I felt reading this book - WOW. I was so pleasantly surprised - oh, let's be honest, it was more like blown away!" -- Holy B. In NC, Amazon Review.