About two years ago I started releasing in local parks and state parks, much better chances of being claimed there and even had two feedbacks on books I left in a local park and a military park so that was nice. I also tend to leave a lot in one of the state parks near my house and nine times out of ten they end up disappearing within a day.
I've also tried campground bathrooms and they always disappear though no one usually leaves a post about them.
Other places I've tried rest stops along highways, a few to a local donation place, a few in random locations scattered throughout my local area.
It's really a game of chance. Now finding books? I've only ever found two and both of those I found in a paperback trade store and how I spotted them? One had the label on the spine. The other one had the label on the front cover. As someone else mentioned try to include spine labels because otherwise they are nearly impossible to locate in such places as paperback trades and thrift stores where some often end up being caught.
As for labeling? I used to just label the inside cover but now I put a label on the spine, a small sticker on the front cover or back cover stating it's a free book and to please take and a note on the inside cover. I also write the BCID number on the inside back cover and at the very end of the book where the story itself ends because I figure if someone reads it and gets to the end then sees the little notation they may be more likely to leave a note here. Someone in one of these forums mentioned they do the same thing so that it catches those who collect books to read at a later date. It might "prompt" them to post here.
I don't know. All I can say is best of luck and try not to get too discouraged if you don't get feedbacks. Otherwise have fun with it! :)