Pyrophobic firefighter

On slips of paper, write down a dozen occupations that fit with your preferred writing genre. If you're expanding beyond contemporary, you don't need to stick with firefighter and doctor so you can throw in zombie hunter or holodeck author. But, even on Mars, they'll have fires and someone needs to fight them. :-)

On another set of slips write down personality quirks (like kleptomaniac, no sense of humor, or superstitious).

Draw one from each set and use the combination as the inspiration of a character or three. Match them up and see what happens.

Brainstorm on the quirks for a bit. You'll be surprised what starts coming out once you allow yourself to loosen up.

If you want to add in some quirks from someone else's brain: 100 character quirks you can steal from me and 100 character traits you can totally steal from me part II. And a phobia list with a bit of story to set them up.