Here's a challenge that's easy to do. It's the Clear Off Your Shelves Challenge hosted by Swapna over at S. Krishna's Books. The idea is to read (1) review books that have been in your house for more than six months and/or (2) non-review books. Library books don't count for this challenge because the idea is to clear off your shelves!
I am committing to 25%, which means that a quarter of the books I read in October and November will count for this challenge. I'd go higher, but I need to leave room for library books and for Echo in the Bones by Diana Gabaldon (likely very long).
Note that Swapna cleverly scheduled this challenge to overlap with the October read-a-thon. If you want to join the challenge, read the full rules on the challenge post.