I wanted to write a book over the summer. Turns out I was a tad too ambitious.

Being the overall nerd that I am, it would be a fantasy.

I have what I feel are good characters in an interesting world. However, I don't have a good story to put them to use. The old quest to find/destroy/save the whatchamacallit whilst fighting the dark lord whats-his-face's evil minions does not work, and I don't want anything generic anyways.

What is a good way/method of coming up with original stories/plots?

Does anyone have any experience? I would be most appreciative of your advice.