While not all books are character-driven, the people who populate your stories are the glue that hold it all together. If your readers don't care about what happens to your hero, what's the point in reading the book? You make your readers care by developing characters that are multi-dimensional and "feel" like real people.
It's easy to slip into the trap of writing characters that are actually caricatures. We tend to, in real life, place the people we meet into convenient boxes (figuratively speaking). Say you meet a sweet, grandmotherly type in the checkout line at the grocery store. You don't stop to think about her past, all the experiences she's had that have shaped her into the person she's become. You picture her baking cookies in her tidy kitchen and giving them to her grandchildren and the neighborhood kids. She probably has a cat. But if you dig deeper, you're likely to find things that will shock you. Remember last week, when we talked about the grandmother who had actually been one of the "Freedom Riders" during the early sixties? Unexpected details like that flesh out the characters in your stories.
When a character first appears in your book, be sure to call him/her by name, unless you're withholding that information for a specific reason. For example, you might start a scene: After wiping her flour-coated hands on a dishtowel, Mildred Stemple opened the front door and smiled at the two little boys standing there. Using your character's name right away helps solidify her in the reader's mind.
Here, the reader's impression is probably "sweet grandmotherly type." And that's okay, at first. But if Mildred is going to be around for more than just the one scene, then you'll need to give her some definite personality traits. You can give her that backstory about the Civil Rights movement if you want, or maybe you'll have her use specific phrases. (In Gone with the Wind, Scarlett's much-used phrase was "Fiddle-dee-dee.") Maybe, when Mildred opens her mouth, she swears like a truck driver. So much for that first impression!
The above language quirk was actually used for Betty White's character in the movie Lake Placid a few years ago. If you saw it, you know what I mean. No one looks sweeter than Betty White, but her character's foul mouth was used to great comic effect in the movie, because it was so unexpected.
I'll bet you know people who defy the clichés. I'll give you an example from my own life: My husband is a truck driver, he doesn't swear (much), and he likes to listen to Danielle Steele audio books when he's on the road. (Now I wonder if I'll hear about this.)
"It took me fifteen years to discover I had no talent for writing, but I couldn't give it up because by that time I was too famous." Robert Benchley