Have joined my mum's book club and she says they struggle with themes for what to read the next month (they all read a book in the theme rather than the same book iyswim).
They have done Bond and "Children's" (children's was a list from a book group suggestion book), horror, "quirky" (Join Me, Yes Man, Danny Yates Must Die, Hitchhikers... I know that list because they borrowed most from me )they have done others too but I can't think what! I feel like I want to kick them to read a bit of fantasy, but they are all very reluctant about the unknown
I'm an English teacher and at the moment we're each reading one of the Booker shortlist for a discussion on Monday before the prize is announced, so something similar - perhaps recent Booker winners (and then discuss their worthiness or not)? Then the same can be done with the Orange prize for fiction and so on.
Do you mean themes as in genres or as in a topic? If the latter, my bookgroup at home has a theme night at Xmas. You could go for colours, food, travel, history, animals...um...that's all for now! Hth.
Gothic fiction is a good autumn one (the right weather for it!) and gives a huge variety because you can go from absolute classics like Frankenstein, Dracula and The Monk to much more modern stuff like The Woman in Black and The Wasp Factory. It also means people who have less time to read can go for something short like Jekyll and Hyde or Poe's short stories.