I have so many hardcopy books and e-books that I keep buying. I'm a bit geeky about my reading (I know targets etc are not for everyone).
For the hardcopy books I can see them and set a target (e.g.2,4 10 books). Then I make a list of a few I definitely want to read and then add in some free choice hard copies to meet my target.
I find this so much harder for my Kindle, because I just keep adding to it (almost 500 on there at the moment), but it isn't easy to see what I have. I can view the list on Amazon but I can only really recall those I bought recently so it is a task to go through and see what I might read that I bought ages ago. I've read that people have randomiser spreadsheets etc but I have googled and cannot work out how to generate something like this.