I choose the books based on what currently interests me. However, since my interests switch quite rapidly, it often turns out that I alternate between highly technical/developmental books and somewhat lighter formats. Today I'm reading about finances, but tomorrow it could be Rodney Mullen's biography.
I tend to abandon books I'm reading halfway through. Perhaps I get bored too easily. However, I often return to the abandoned titles after a few months, review the highlights and notes, and continue reading.
I use goodbooks to lookup what books on a given topic are good enough to try.
I have lots of unfinished books on my plate. When I want to get back to one, I create the book notes from the highlights I already made to remember what the book was about and continue reading from where I finished.
To make book notes I export the highlights to HTML file and process them one by one in code editor (I've created my own converter from Kindle's HTML format to JSON).