Secondary Doesn’t Mean Second-Rate ~
Your main characters run the show, they are who your reader falls in love with or love to hate. What helps define and make these characters three-dimensional aren’t just the words you choose, showing instead of telling, attitude, etc. – it’s your supporting cast of characters.
Every character in your novel should have 2 things: a purpose and a personality.
How your main characters interact with everyone else is only one side of the coin – how everyone else reacts to your main characters says a lot about the relationship between people/entities and themselves.
Every character has a function.
If you find that the next door neighbour who says, “Hi” in only one scene is there without a clear purpose – delete him. If there’s a reason you need that neighbour to say, “Hi” then make sure the impact of the event is apparent. Have it be a ritual every morning and then readers will see how this persistence in the secondary character affects one of the main characters, or the absence of this neighbour sends a warning signal and helps build suspense.
So what about those characters who don’t have names?
The ones who bump or jostle the protagonist in a busy hallway or people the cafe where the antagonist is sitting and scheming are background characters and still have a clear job to do. The guy who bumped your protagonist may never be seen again but your protagonist is still affected (or not) by being bumped. This random guy’s purpose was to expose and make relevant the intensity of the main situation or show off an important attribute in the building block of the personality of the protagonist. And the crowd at the cafe? They act as a single entity – your antagonist will either try to ignore them successfully or not and this will affect her in a meaningful way. If it doesn’t, then make use of your location to influence the reader’s understanding of the character or situation or cut the scene and try it in a different location that will have an impact.
Don’t leave anything to chance – it usually becomes filler and does not enhance the story in a meaningful way. Use that scalpel carefully: trim the fat and tighten your prose for impact and purpose.