Multiple viewpoints in a story can be very, very confusing. Especially when they switch at seemingly random times or when there’s too many of them, it can be hard to find out who is telling the story at the moment, through whose eyes we see what is happening. Yet, they can also be necessary.
In most stories, there is only one viewpoint character, no matter which kind of viewpoint (first-, second-, third-person, close or distant) there is. The only real exception from that is the omniscient narrator who knows it all. Yet, omniscient narrators come with a host of problems of their own, so having a viewpoint character who also has a role in the story is usually the better choice. It brings the readers closer to what is happening.
Yet, if you have several viewpoint characters, the switch between them might be jarring for the reader. Suddenly, they are in another place and they might not realize that they’re looking through another character’s eyes, so they wonder what happened. This gets especially weird in first person because there’s no easy way to introduce the new viewpoint character by starting the first sentence with ‘X went into the room’ or something similar that tells us X is now our viewpoint character. In first person, you do not have the chance to do that because a first-person viewpoint character will usually not refer to themselves in third person. It can help to use some symbol in the scene breaks, but it will still be trying and can easily lead to misunderstandings and confusion.
Even if you are using third person for your story, there are still a few things you should keep in mind.
First of all, you should never switch viewpoints within a scene. If you start a scene with character X and switch somewhere on the way to character Y, people will definitely get confused. Never switch within a scene, begin and end it with the same character and don’t make any switches in-between.
Another thing you should avoid is retelling a scene several times with different viewpoint characters. That can get repetitive and confusing very quickly. Imagine finishing a scene and moving on to the next, only, in a “Groundhog Day” move, you are back where you started off before - the beginning of the scene you just finished reading. This time, you are looking at the same things which you’ve already seen happening, only from the point of view of character Y instead of character X.
For every scene that contains several potential viewpoint characters, choose the one who has the most stakes in it. Only retell a scene if it is absolutely necessary (which it rarely, if ever, is).
Another thing that helps to avoid confusion is to give every viewpoint character a distinct voice. Like this, readers will come to recognize the voice and know who is talking, even if they’ve somehow missed the switch.
A distinct voice contains different things, such as the choice of words, which has a lot to do with the age and social level of a person, but also what the person notes most clearly - smells, sights, sounds, specific objects or people. It’s hard to come up with specific voices for many different characters, though, so be aware that it will be hard to tell your epic story through the eyes of twenty different people who all have a distinct voice.
If you only have two or three viewpoint characters, giving each of them a distinct voice is definitely a possibility and it will work out well enough with first-person viewpoints as well. If your two first-person narrators both have a distinct voice and you introduce each of them when first using the viewpoint, the reader will quickly realize when you’ve made the switch and know who is talking at the moment.
When it comes to choosing who gets a voice in the first place, the very first question is ‘does this character’s viewpoint contribute to the story?’ Now, you’re probably immediately shouting ‘yes!’ at this, but take your time and think it through.
Every viewpoint character demands of your readers to remember details about somebody else. Every viewpoint character has to matter to the readers, too, or there’s a chance they might just ignore the chapters or scenes the character is narrating. To matter, a character must play an important role in the plot and their viewpoint must add to the story.
Say you have a story with three viewpoint characters. One is a brigand who took a book from a group of travellers, all of whom died trying to protect it. He can barely read and not understand more than the list of names in it - he has no idea what those symbols and diagrams mean, but it must be worth something. The second one is a magistrate tasked with finding the ones behind an intrigue to kill the king and replace him with his much-easier-to-influence son. She knows that the people behind the intrigue will have put everything down and learns that some men she suspects to be part of it have been killed by a brigand, so she’s hunting for the brigand. The third character is the leader of that group, the mastermind spinning the intrigue. After learning that those men were killed, her main goal is to recover the book - by violence or money, whatever it takes.
All three of those characters have their own plot to follow and the plots, all revolving around the book the brigand now has, will converge eventually. Perhaps the brigand and the magistrate will team up and bring down the mastermind behind the intrigue (enter romantic sub-plot here, if you wish). Perhaps the brigand will side with the mastermind for money and make a try or two on the magistrate’s life (enter redemption for the brigand here, if you want). In a highly unlikely turn of events, the magistrate might be corrupted by the mastermind and join her in the search for book and brigand to make everything happen as planned.
All three characters have their agenda and all three characters will have separate stories to tell before the great finale happens. In this case, the three viewpoints are called-for - none of the characters can tell all of the story that is necessary to bring their arcs together.
In the example above, the three viewpoints are necessary because there are a lot of important things which happen and can’t be told from the same person’s perspective. The brigand has no idea about the magistrate or the mastermind, he only knows he has this book and wants to turn it into coins. The magistrate doesn’t know who the mastermind is and only knows the location at which those men died, so she doesn’t know which brigand to hunt down to pick up what they had with them. The mastermind, too, doesn’t know who the brigand is and can’t easily approach him with an offer or a threat, neither might she know that the magistrate is already after her and her co-conspirators. If only one viewpoint were in the story, a lot of things would happen suddenly and without warning, because two-thirds of the story would happen behind the scenes and be told after the fact or never at all. That would be aggravating and confusing - two things a story should never be.
Major things which happen need to happen on the page of the book, not somewhere behind the scenes. If your plotting demands that the viewpoint character isn’t there when something important happens, you might have to introduce another who can witness or take part in those parts of the story. Either that or you have to re-plot the story to make sure the viewpoint character is included in those events.
Multiple viewpoints are not something you should introduce into your story lightly - many stories will do well with only one viewpoint character. Yet, there are stories which span a wide range of space or time and need several viewpoints to be told. It might even be just that one scene you need in your book which needs to be told from another perspective in order to include an important bit of information your viewpoint character just can’t get otherwise. Be careful about introducing various viewpoints, but be aware that it can be necessary, depending on your plot or plots.