I always do something on my days off, even something small, that makes the day feel somehow different from an average day. It can be really tempting when you're tired to just stay at home in your pyjamas but the days quickly melt into one and so you don't really feel like you're getting a break.
Sometimes I drive to a totally new place with a picnic, or cook a meal I've never tried. Sometimes I plan bigger things but the most important thing, I have found, is to stop the days bleeding into one by doing something that makes each day feel a bit different somehow.