Not all of your characters have to be developed equally. While some need a rich sense of background, history, and motivation to help propel the realism of the story, others are side players. You want them to seem real, but at the same time, they don't need to command the reader's attention in the same way as your lead characters. In fact, it can be distracting, and slow the pace of the story, if you spend too much time on detail about characters of secondary importance. Even veteran authors fall into this trap at times. Let your spear carriers be just spear carriers.

A bit of carefully chosen detail may be all you need, depending on the character's degree of prominence. It's always useful to provide a few distinguishing characteristics, to lend realism—and to help the reader remember the characters, if they're going to reappear. For example, "The guard wore a perpetual scowl and slurred his words as he spoke..." may be enough to bring the character into relief, and to give a point of reference if the "scowling guard" needs to make a reappearance.

Look for the Unexpected

Let me leave you with this thought before we move on to a challenge:

Your characters will always be more interesting to the reader if you can find something about them that is unusual, quirky, unexpected. Try to avoid the cliché, the tired reworking of old themes. Think of something that will make the reader sit up and take notice, or chuckle, or go, "Whoa!"

A Wrinkle in Time

Always keep this question in the back of your mind: Have I seen this before? If the answer is yes, maybe you need to think a little harder about your character. If the answer is yes, about a hundred times, maybe you need to think a lot harder.

Don't be dismayed if it doesn't all come together at once. Like everything else in writing, characterization can take determination and effort to get right.