The easiest way to make a support character feel like a gratuitous plot-enabler is to make them a stereotype, to fill the same sort of niche we always see them fill.
“A rude waitress has to spill the coffee on her so that she has to go home and change clothes and that’s how she avoids being downtown when the aliens attack.”
I’m tired of the rude waitress, the inept cop, the mean teacher, and the insensitive doctor. On the whole, people with these behaviors don’t tend to stay in these jobs very successfully, or very long. They’re used as exceptions, because there’s humor or drama or something eyecatching in the exception, but the novelty that drives these exceptions and makes them interesting is lost when the exceptions become the norm. Then they just become plot devices, and it shows.
When you use a cliche, ask yourself why you’re using it and if it needs to be there. Chances are that it doesn’t, but if you really want a character to be a stereotype, just find an interesting way to use the device. Give them a reason for it. They could start out okay and have their behavior degrade over time, for some interesting reason. They could realize their trouble and try to grow and change, and let the reader cheer them on. Or there could be some reason for it that we discover, that helps us understand why they behave the way they do, or why they’re in the job they’re in despite not being a great match for it. The police chief hiring his inept son as a cop has been done a million times, but at least it supplies a reason for the cop to be inept.
I’d rather see a bad guy elude a skilled cop — that takes more talent! I’d rather see a well-meaning waitress spill coffee on someone and feel awful about it. That adds more to the story. And I’d like to see the conflict in a sensitive doctor who still has to deliver bad news. That’s where a minor character shines and brings depth to a story, even if they’re only “on screen” for a couple of pages.
