I typically just steel myself and go through the current book I've chosen. Unless the book is so bad I return it, I take it piece by piece.

A good mindset I get in is thinking about how while I may have a lot to do, if I do a bit of each all at once, nothing will get done.

So just take every book one at a time and think about how far you've read, rather than how much more you have left. It's a great way to positively reinforce your reading habit.