read erotic stories by the window (preferably while dressed in a cute little slip dress or similar).
listen to burlesque music while you get dressed. notice how your body responds.
make a list of sexual things you want to try & do one of them. (surely not all the things on your list will require a partner!)
stare at yourself naked in the mirror, focusing on the parts you like best, until you thoroughly love what you see.
stand in the rain & think about wet lips.
listen to naughty podcasts on a long walk.
eye up attractive people & ponder what they look like under their heavy raincoats. (people wearing maid-of-the-mist-style ponchos are exempt from this, obviously.)
try to get into the mindset of someone who has a rain-related fetish (rainboots, raincoats, etc) & observe the way you feel when watching people. (just don’t be a creeper, little one.)
write a sexy story that takes place on a rainy day.
listen to smooth jazz while naked.
take advantage of the lovely overcast lighting & shoot some risqué self-portraits.
flirt with some internet stranger who lives thousands of miles away.