Unsurprisingly, major characters are the ones who are the subjects of much writing advice on characterization. They’re the ones readers are most likely to notice and remember, because they are onstage the most and have the most impact on the protagonist and the plot. In an ensemble-cast multiple viewpoint story, they’re the ones who have most of the POV scenes and who recur as viewpoint characters (secondary characters and the occasional minor character almost never get to be the viewpoint in a scene unless they get killed at the end of it). Major characters are usually the ones who have identifiable roles that slot into the story structure: the Sidekick, the Mentor, the Hooker with a Heart of Gold, etc.
Therein lies the source of a good many of the problems with this particular crop of characters. Because they inevitably fill particular roles in the story structure, and because most of those roles have familiar, well-defined personalities associated with them, it is terribly easy for the writer to just fall into using those roles without examining them too closely. It’s especially easy when the writer is uncertain about his/her ability to write “good characters,” or to write that particular type of character well. And if the writer is occupied with a particularly stretchy plot or structure, or focused on pulling off something tricky with one of the other characters…well, it’s a whole lot easier to grab Plucky Comic Sidekick #4 off the shelf and shove him/her into the story so there’ll be one less thing to break their brains over.
This isn’t necessarily all bad. If the writer is doing something tricky or stretchy, going with the tried-and-true tropes for a couple of the main characters can free up enough brain cells to let the writer pull it off with panache, rather than succeeding by the skin of his/her teeth. If the plot or protagonist or setting or style will be new and experimental for readers, having some of those old, familiar types running around can provide a firm place from which the reader can understand the rest of the story. And if the writer is juggling a huge cast it is easier for both the reader and writer to keep track of familiar personalities.
Also, using old, familiar character tropes in a new setting or situation can make them seem fresh and new…and if you’re combining genres, there will probably be readers who haven’t seen those types before. After Caroline and I wrote Sorcery and Cecelia, we got ton of comments about the characters. Half of them complimented us on how wildly original they were; the other half (who obviously read the Regency Romance genre from which we had shamelessly stolen a boatload of stock characters) said how cool it was to see such rusty old clichés given new life by moving them into a fantasy setting. It can be a win-win.
Most of the time, though, taking the easy route is not the most effective alternative, and therefore not really what the writer wants to do. If one drops into a standard character trop for a secondary character, it’s not usually a big deal, because they have so little stage time that it hardly shows. For major characters, though, it gets really noticeable really fast. Avoiding the problem is not always as easy as it looks, though. As Lois Bujold says, “If you can’t see it, you can’t fix it,” and it can be surprisingly hard to spot the places where one is inadvertently or unconsciously dropping into those old, familiar ruts.
The first step is to look for it. Even if you are absolutely positively certain-sure that you would never, ever stoop to doing such a thing. Because you could be wrong, and if you never look, you won’t see it, and if you don’t see it, you can’t fix it. Critique groups and first-readers are enormously useful in this regard. If you get in the habit of stopping for just a second when a new character shows up and checking to see whether they are behaving as a standard character type, you can decide right then whether or not to keep the character as that kind of standard trope or change the way he/she presents. Or, if you are the sort of writer who gets to know your characters as you write them, you can come back after the first draft and, during the revision process, upgrade their initial couple of appearances to include hints or references to stuff you only found out much later in your writing process.
Looking carefully at those first couple of scenes is actually a good idea for most writers, because even those who plan very carefully tend to see the characters differently after spending 100,000 words with them. This isn’t something that one can do purely by instinct, though, because major characters are also ones who can be affected by the events of the plot. It’s not just the protagonist who can grow and change during the course of a novel (or choose to remain steadfast in whatever their convictions are, and take whatever consequences result). Major characters may not look the same at the end of a novel because of the events that happened in the novel, not because the writer has gotten to know them better. Revising the opening section is therefore something that has to be done with care and thought – lots of thought, thinking is good – in order to avoid making the George of Chapter One into the George of Chapter Twenty-One, when what you really need to do is make the George of Chapter One into someone who can become the George of Chapter Twenty-One…and without taking the story over from the protagonist.