You have a plot in search of a cast. Ever notice how so many story folks sound alike? It's the same way comic books denizens look like brother and sister; the artist draws them with the same consistency as he signs his signature. We need to mine a little deeper for characters who've left their marks on us.
Real People Here you get a unique vocabulary, pet words, mannerisms, style and slang. But don't let your character become this person to the detriment of his role in the story. Shy away from celebrities and those who might recognize themselves. And we don't want our cast too real, nattering off down side streets the way we do, because they have to stay on script. A surprising number of authors on the Amazon forum admit to doing this (what, me?), though it has to be disclaimed on the copyright page.
Books and Magazines Lorna Doone was the model for my virtuous wizardress, but being wimpy and boring, the Lorna model needed a dash of fire and determination. Sometimes a face in a magazine will be just the look you've pictured for a character, whether major or minor. When an enigmatic wallet photo of a woman fell out of a library book, a forgotten bookmark, I was off and running with a story about a succubus who snares victims with a cursed photo. Sort of how the curse was passed on in the film Night of the Demon. You have to get some other chump to accept it. For the record--no, she didn't get me.
Video Games Funny glitches in the PS2 game Summoner prompted the model for my quirky sorceress. This gal threw fireballs that clipped her own teammates, got left behind when doors closed on her, and disrupted cut scenes with noisy and spectacular healing spells. Oddly, the king didn't seem to notice this disrespect.
TV, Film, Occupations Science types are precise and logical; foreigners may pause to search for the right word (for accents, a little dab'll do ya); and let's not forget your own skills and experience. In the ghost story The Invited, Jennifer McMahon's protagonists Helen and Nate carry out much of their dialog while building a house. The author creates a married couple imbued with her own skill set, which grounds them in their DIY personas. The wife's quest for haunted building materials is a major subplot. Find the characters hiding in your own attic for memorable stories.