Inspiration, that is what we are all looking for when we sit at our desk or computer to write a story. I remember reading somewhere that J.K. Rowling got her inspiration for the character of Harry Potter when she was on a train and a boy in a cape walked down the aisle towards her. It seems we just need a tidbit and the imagination steps in and says, "I've got this."
Personally, many of my characters have come out of my past from people I have known either through work or some other encounter. If the personality is strong enough to leave an impression on me, they just might end up in one of my stories. For a new collection of short stories that I'm writing I dug way back into my past. There was one or two incidents that stuck out for me with each of the characters and from there I developed a story. So, besides a character I need to have a little bit of information about them that in some way, whether negatively or positively, inspires me.
The story either writes itself quickly or I may struggle through it a bit. When that happens I just let it go and move forward onto something else. When I finally get back to it, after the story has had time to stew about in my mind, surprisingly to me the rest will unfold and go places I hadn't thought of it going.
I've also found characters while at dinner in a restaurant or in line at the supermarket. There might be something they do or that I overhear them say that will work nicely in a short story. Perhaps their role is that of the minor less developed character. My major characters are more apt to come from a person with whom I am more familiar, but not always. In a novel I am currently working on the two main characters were created from two people I had a brief encounter with at two different department stores. Both of them were cashiers which was all I needed to create a novel where they fall in love.