Take every person you've ever known or had a notion about, preconceived or otherwise, every face, famous or not, every voice, every name, everything you've ever seen or interacted with that has to do with a singular human being, be it a celebrity and your idea of who that person is, a family member or friend and your direct knowledge of the kind of person they are, or the lady across the street you buy Cigarettes from. bring these people to the forefront of your mind, and then mash them together.
turn every single face into one, every single soul into a single being, and describe this person. describe what kind of person they are, i'm not just looking for good or bad, i'm looking for as descriptive as you can possibly get. be writers about this. the idea is that this is using everything external to realize something very internal. keep that in mind. dont hold back.