When writing multiple viewpoint novels, one of the things you have to decide is which characters are going to be viewpoint characters (and which ones are not). You also have to decide which character you’ll be using to filter each scene through (i.e. whose viewpoint to use for each scene). These choices are particularly important when using character-narrator voice (first person and third person close/intimate narrative).
Let’s talk about choosing your viewpoint characters first.
Who is the story about? Does that person have to be a viewpoint character? No. Watson is our “reporter” viewpoint character even though Sherlock Holmes is who the story is about. We don’t want to be in Sherlock’s head because (a) he’s a little nuts, (b) his eccentricities would make him hard to relate to without Watson filtering him for us, and (c) we would know early on “who dunnit,” thereby cutting the story short. Even if written only in author-narrator voice, filtering Holmes through Watson allows us to empathize via Watson who is his friend and cares for him, thereby making us do the same.
Typically we choose viewpoint characters who are sympathetic and relatable and who have stakes. And we don’t choose characters who are not sympathetic (such as villains), even though sometimes we do write them because we need to show the reader what they know. Or we show them in order to contrast and compare. Generally however we want to stay out of the heads of the despicable—no one wants to read about a child molester lusting after a child.
Not using a certain character as a viewpoint character is a legit way to hide information. If you decide not to use one for this reason, don’t pop them in at the last moment for a reveal or you risk pissing off the reader because it’s going to come off as a deus ex machina. If you want to do the “reveal” via dialogue that’s fine. Just have them speak the information in a scene told from an established viewpoint character. Then it won’t feel like you cheated the reader.
Another reason to use a viewpoint character is because they are the only witness to an event. But if you’re going to do this, do it sparingly. If at all possible, it’s better to have them report it to an established viewpoint character than to just have one scene from their point of view. Why? Because then you’ve given us a spear-carrier with no arc of his own as a viewpoint character. Do this more than once or twice and you dilute the story.
When it comes to which viewpoint character to use for a particular scene things get a bit more interesting.
Using the character with the most to lose is good, but it’s hard to stick to this if you have multiple sub-plots, especially ones run by secondary characters. The whole point of having multiple viewpoint novels is that you don’t have to stick with the protagonist.
So what if two viewpoint characters are present? Should you always pick the one with the greatest stakes? What if you need to convey information that only the other character has? Then you should pick the other character, the one who knows more, or can provide another perspective. Why? Because doing so puts your reader ahead of the protagonist and that can be used to build tension, the reason that your reader turns the page. If you want the person with the most at stake to have the same information, then stick to his viewpoint and have the other character tell it to him. But if you don’t want him to have the information, then give us the other perspective.
Switching to another viewpoint is also a very useful technique when your protagonist is doing something “bad.” By providing the reader with a filter (via another viewpoint character a la Watson) you are allowing the reader to remain sympathetic even when the protagonist may be doing something questionable. By looking at it through the eyes of a character who can still love, admire, or respect the protagonist who is doing something questionable, you’re keeping the reader’s sympathy towards the protagonist intact. It’s one thing to have the protagonist justify his bad deeds to himself and quite another to have someone else see it as necessary or justifiable.