Over the last eleven years, I've used so very many 'themes' when doing my pages, that it's often hard to come up with a 'new' idea.
For example, here are some themes that I've used:
Colors--my favorites: Mauve and Teal
Cats--photos of cute cats in general and 'my cats'
Science Fiction--my favorites in general, then Dr. Who, & Star Trek
Oceans/Ocean creatures
Unicorns
Fairies
Seasons and Holidays
Christmas: one year I had all Christmas trees on one page & something else on the other one
I always do screenshots of my pages, so that I'll remember what I've done! I now have a very big folder of those screenshots.
I'm still not sure what I'm doing this holiday season. For now, I have 'winter' on one page--but nothing yet on the other page. Right now, I just have a pretty DocShell layout on that page--mainly so others will remember that Shell, Barbara, Pamela, & Elizabeth, etc. have always been there for us--and are still making pretty layouts!