I love writing prompts. I have the writing.com app that generates prompts in a variety of ways (It's $1.99, but totally worth it, IMO), or I'll browse Pinterest, or if I'm feeling particularly adventurous, I'll just google "writing prompts" and see what comes up.
I love that they're zero pressure, but still valuable, because time spent writing = practicing. I've gotten tons of decent short stories out of prompts, one novel, and a massive file full of garbage.
Prompts let my brain relax and play for a while, and then I can get back to my real work on my WIP.