Plot ideas : I love trees. Ok that's a bit broad; I love especially the connection between trees and spirit. The idea of trees being full of animus of some kind - probably harking back to CS Lewis and talking trees and Fangorn, and hamadryads. I remember once reading Findhorn Garden and getting a glimpse of a whole unseen world of nature linked spirits and creatures that you could see and interact with (as ROC did) if only you were in the right state or frame of mind.
Also I'm a hopeless romantic, so there would have to be a love story in there somewhere and it would need quite a bit of angst and tension. Perhaps forbidden in some way or fated not to go so well. Maybe from different worlds, certainly stumbling over misunderstanding each other sometimes.
A long time ago I read a short story, I think it was by James Blish but I've never found it again, in spite of hunting for it many times. It involved someone who met a woman who had violet eyes who was from another universe. And when he was in her universe she looked like sort of messy lines and when she was in his world she looked like, well, a woman with violet eyes. Now that would be strange and hard to get used to. Could I live in a world where when I looked at the women I loved I saw messy lines? And what would it be like for her in my world seeing me as a blobby body instead of normal messy lines?
And I love myths, especially Celtic ones. I love the way Charles de Lint weaves elements of these into his stories; I'd like to be able to do that.
And cats, there would need to be cats.