This is my favourite writing prompt of all time. If I'm stuck for inspiration or I want to create a character, I usually turn to this prompt. I'd been trying to ages to find where I'd got it from so I could share it, and I finally did. It came from Kate Long, who I follow on Twitter.
It goes like this:
1. Imagine a coat on a station platform with 5 items in its pockets. You decide the style of the coat, the platform, and the items within it as a precursor to sketching your character.
2. Begin creating an idea of the motivations of your character. Make three statements about the person that wore the coat based on the items in the pocket.
3. Write for 10 minutes, without stopping to edit, review or re-draft. Flesh out what you’ve found out about your character by putting them in a departure lounge of an
airport, inside a busy restaurant or in the bathroom brushing their
teeth in front of a mirror.
I usually use this as a basic starting point. The coat and the items in the pocket always come in useful, but sometimes the coat is being worn by someone, not left on a platform. Sometimes an idea from one of the items gives me an idea that I run with. If I'm really lost for an idea then I'll put them in one of the situations above, but usually something else will inspire something for the 10 minutes os writing.