For Each Scene, Picking the Viewpoint Character
Each scene in your novel should be narrated throughout by a single character. If your novel is written throughout from a single viewpoint, either in first person or in third, then the same character narrates every scene. But if you are writing from multiple viewpoints, with different characters narrating different scenes, then there may be times when more than one of your narrators is present in a scene. Then, your challenge is to decide which of those characters is going to narrate the scene. Which one do you pick?
OPTIONS FOR PICKING A CHARACTER TO NARRATE A SCENE
Pick the character with the major role in the scene, or
Pick the character with most at stake in the scene, or
Pick the character who is thrown most off balance by what happens in the scene, or
Pick the character with the most interesting and complete vantage point
If you're not sure which character should narrate, then write two versions of the scene, one from each character's viewpoint. Decide for yourself which one works better. What is gained and lost by allowing a given character to narrate instead. Which version better holds your interest? Look at the big picture, too: Which version reveals to readers what you want them to know at this point in the novel and keeps hidden what you don't want them to know. Then be sure to save the version you like least in your Out file just in case you change your mind.
How Many Viewpoints Is Too Many?
It is possible to diffuse the emotional impact of your story with too many narrators. For readers to keep reading, they have to care about the protagonist as well as about the story you're telling. If you give them too many competing narrators, they won't know whose story to pay attention to. Readers who stop caring stop reading.
There is no maximum number of narrative viewpoints. You need as many viewpoints as are necessary to tell your story. The commercial blockbuster The Da Vinci Code has at least five viewpoint characters, including the villain. In Toni Morrison's Pulitzer-winning novel Jazz, about a half dozen characters take their turns narrating in what ends up feeling like the theme and improvisation of a jazz ensemble. William Faulkner's tour de force As I Lay Dying has fifteen narrators, the members of a family carrying Addie Bundren's coffin to where she wished to be buried. Even the dead Addie takes a turn as narrator.
Never add a viewpoint character just because you feel there's something important you have to tell the reader and none of your chosen viewpoint characters are privy to it. Find another way out of that dilemma. Viewpoint is too powerful to bestow for such an artless reason.
The only way to know if you have too many viewpoint characters is by gathering reader reaction. This is why having trusted readers give you feedback is so critical.