Every story needs depth. There are several ways to achieve this. Today I have decided to shine the spotlight on those with smaller roles.
Who am I referring to? The minor characters--or side characters.
This can be your hero's goofy sidekick, or the quiet neighbor who doesn't even have a name.
In a story, just like in real life, every character--both great and small--has a purpose. If they don't, they shouldn't be in your story to begin with.
I'm serious. If they're there just to be there, take 'em out. Few things will annoy a reader faster than a useless character-- (not to be confused with an INTENTIONALLY useless character--if their role is to be horribly inconsequential and cause trouble for the hero, then by all means milk that for all it's worth).
Today I'm going to skip the SIDE characters for now and just focus on the BACKGROUND characters. (you'll often find them even further to the side than mere side-characters.)
These characters are not only nameless, but often faceless too.
If your hero is walking down a city street, odds are that he's not going to be the only one up and moving. But even though none of the passerby have a known name, they have a purpose. They complete the scene. Without them the scene would feel empty. (Unless the city is abandoned. In that case, carry on...)
But again, I caution you to make sure you give said background characters the attention--as their author--that they deserve. Even though your readers, or even your hero, may never know anything about them, it's important that YOU, the writer, DOES.
That gruff guy in a suit who brushes past your hero? He's late for a meeting.
The girl walking her dog? She's been walking for an hour because she's afraid to return home and find her family still arguing.
Why should you do this? Because it adds depth. Even if you don't mention anything like the above, there is something that happens subconsciously as you write that makes the background characters come alive at just KNOWING this information. I have found this to be true from my own experience. Treat them like real people, and they become real.
Even better is that in doing so, I sometimes figure out a small plot twist--or a plot parallel that changes the course of the entire story. And it was all thanks to the fact that I gave that one background character an identity.
For example, in the book series that I'm working on with my best friend (aka: partner in crime: Adelaide) there are many guards who do nothing more then guard things. (so profound, I know.)
However, there was one guard in particular that we would use in random scenes to help move a story point along. At the time this guard had no face, no family,--basically no identity whatsoever--except for a first name. It wasn't until we looked into said guard's backstory that he suddenly came alive. He is now a VERY important and influential character in the series. He even has his own character profile on Pinterest. Many of the ideas that followed wouldn't have occurred if we hadn't treated him with the same developmental depth as one would a main character.
Needless to say, background characters are very important. And sometimes, they even have a few secrets of their own.