There are many different places to look to for inspiration.
Look within. Of course. Ideas are lurking there, frequently brushed aside for consideration on some other day. Now is a day to give them deeper reflection. Just pick any one and make a stab at it.
Events happened today. Who did you see? Someone passed by might have been memorable, or sparked some odd memory, or set off a string of imagined lives. Where did you go? Remember what it looked like, smelled like, sounded like. Allow a reader, or a spectator, to be there too. Description. Poetry. Recorded sound. Music. Scents. Create the movement. Imitate moments, then distill, abstract, exaggerate, deconstruct.
Look out. Someone across the world would be surprised by a letter from you. What do you need to say? Send a mysterious message. Know who you are writing to, keep it a secret, but share with all.
Sooth some pain. Make peace with that awful thing you did. Or that virtuous fight. See the other point of view, give it honest consideration. Argue against yourself. Come back around if you will.
Take a picture. Or find some old photo. Start from there. What happened, or what might have been?
Go out to get some inspiration. Watch more plays, see more bands, go to the park to watch the kids play, put on some music, read a new book, re-read an old one, read a magazine with a critical eye.
Look back at the work you've done. What did you mean to say, but forgot, or got side tracked? Say it.