I've been there myself plenty of times. My suggestions would be to vary your daily routine (don't take the same route as you usually do), take a day trip somewhere new, or shoot early in the morning or late at night. Oftentimes just a change in lighting will give new perspective even to subjects you've seen a million times. I also find this time of year especially challenging here in New England where I live, when there is so little color outside and everything just looks, well, blah.
I'm not sure this addresses your question about ideas for sets/series, but for me those things tend to take care of themselves when I am shooting frequently.