Don't ignore them. They can make or break a movie, a tv show, and definitely your book. Take this episode of Castle. "One Life to Lose" aired Monday, March 21st, with Jodi Taffel playing a soap opera fanatic. Costuming certainly helped--jingly bracelet over cuff, curly hair wild like her eyes, long nails weilded like daggers. But it is Taffel's timing and expression that steal the scene. Check her out below at 10:24.
If a minor character has character, your scene can come alive. A reader will laugh or cry with that character and exclaim, "Perfect!" if you pay attention to the little things and the little characters. Just like the setting and the costumes and the framing can play essential background to the main characters, they can also play starring roles.
Let your minor characters shine through! Do any favorite supporting roles come to your mind?