Any good fiction includes great characters. To develop those unique individuals, you need to know them. The easiest way to know them is to base the character's traits on the ones you admire, or dislike, in people you know.
When you have a character that is the personification of Great-Aunt Maud, think about phrases she has used, ways she used body language, how she sounded, and favorite smells - like Mrs. Violet (Jones), a third teacher in the primary school I attended, who always wore a cluster of violets and smelled of lavender cologne. Also, think of what might have frightened her or motivated her for good. What were her favorite foods, music, books and movies? How did she sound when she spoke and laughed? How would her touch have felt? If you describe all of these, your readers will know her too.
In Smoke from Distant Fires, I know how Millie thought and acted because she is based on the traits of my mother. I simply introduced her to my readers. In my short story, Christmas Feathers, which will be out in the middle of October, James and Rachel Bryson are very dear to me because they were my g-g-g grandparents. Naturally, I never met them. Although, at the end of a very long day, it feels like I may be old enough to have known them personally. I read about the time in which they lived, the County History, and have heard enough family stories and observed family traits, to "know" my characters. If you know them well and describe them equally well, your readers will know them too. Introduce a friend to others in your next book.