A month from now we will be celebrating Henry’s third birthday. He was born shortly after my father died, on my father’s birthday. They couldn’t be more dissimilar. My father was insecure, sometimes resentful, often angry. Henry is a smiley-faced little boy who brightens our lives with his cheery personality. Those are differences which, I suppose, is symptomatic of the general pattern for human life.
When we create the characters that populate our novels we look for variety. Think of the differences in the Bennet sisters. Had they all been like Lizzie, the story would not have worked. But how do we, as writers, make our characters different? Well, that’s when we get back to the old, old advice of “show, don’t tell”. We show the differences in the way the characters behave.
Take a problem, show it to your characters and look at the way they react. For example: a guy backs his car into another one standing stationary. Now imagine each of your characters inside the victim car. One flies into a raging temper, another tackles the matter patiently, a third bursts into inconsolable tears. Three different characters and three different reactions. I haven’t described them, but you should be able to picture them in your mind simply by the way they behave.
You don’t have to incorporate that particular problem into the story, of course, simply keep it in mind when you write about each of those characters.