Observe a person you don't know well. A forgotten relative in old family photos, a stranger on the street, just someone mysterious and unfamiliar. Adlib for the person's thoughts for the moment you see them. Then write about your own thoughts on something and have your stranger respond or think about them also. Basically, create your own character.
Write a love letter in any kind of tone (silly, fantastical, real). Leave it in a library or bookstore.
This weekend we'll have responses to Prompt #2!