Stolen from the internet, specifically rionaleonhart and auto_destruct:

1) Make a list of fifteen characters first, and keep it to yourself for the moment. (That way you're not leading the questions asked to fit the characters.)

2) Ask your flist to post questions in the comments.

For example:

'One, Nine and Fifteen move in together. Is this a really bad idea?'
'Under what circumstances might Five and Seven fall in love?'
'What would Two experience in Silent Hill?'
'Why is Eight so very, very angry?'
'Write a drabble in which Three and Eleven FIGHT CRIME.' (...possibly not technically a question.)

3) After your flist has asked enough questions, round them up and answer them using the fifteen characters you selected beforehand, then post them.

...

Just so you know, there will be four Jacks in this list.