Here are the key things you need to consider to ensure you do Points of View (POV) right.
Imagine if George RR Matin's A Song of Ice and Fire was written from only Jon's perspective — we'd miss out on the incredible scope and history of the world. Now, imagine if Catcher in the Rye by J. D. Salinger was told from many perspectives — the isolation which Holden feels would evaporate and we'd see him more as a selfish jerk.
POVs are important; getting POVs right is key to the success of your narrative.
First, think about if you need additional POVs
Does your story lend itself to multiple perspectives, or is it better suited to just one? Think about what you’d gain by adding an extra POV, and what you’d loose.
Multiple POVs lend themselves well to fantasy and sci-fi — they allow writers to quickly create a universe built on the experiences of many characters. Multiple POVs suit epic tales with a large geographical scope, where action is happening planet-wide.
One POV can feel more intimate — the reader is trapped with that character and they experience the world through the character's eyes only — they work well in romance, detective and thriller novels. The writer is better able to establish an unreliable narrator because there are no other perspectives to challenge the POV.
One POV per well-structured chapter
This is largely personal preference, but I prefer not to jump around into other people's heads mid-chapter — it gets confusing.
Make sure your POV chapter has a clear beginning, middle and end — it is likely that the reader won't read about that character for a while, so it is important to ensure they have a satisfying conclusion to the conflict in that chapter.
There is nothing worse than reading a cliffhanger ending to a chapter, and then switching to another POV without getting a satisfactory conclusion. The reader will spend their time reading the new POV wishing they could find out what happened to the the last character they read. Of course, this doesn't apply to POVs which are directly connected to the events of the last chapter and can show the answer to the cliffhanger.
Establish a distinct, clear voice for each character
Differentiate the voice of the character as much as possible.
Make it your goal that a reader is able to know, just by the writing style, which character's POV it is without reading the character's name or without a chapter title.
A voice is established not only in the grammar, but in the words you choose, and in what details the character focuses on. George RR Martin is someone who does this incredibly well. In Catelyn Stark's chapters, she focuses on the emotional impact of the events — she is a mother, after all. She notices the details that a mother would notice, such as "good birthing hips" on a woman. Jon Snow, a warrior and a bastard, notices the tactical layout of the land, the quality of someone's weapon. His words are more direct, hard and cold like the way he's been treated in life.
Select the right character to include as a POV
Don't just add a POV for the sake of it. Think about what insights the character’s perspective brings to the table. This perspective should connect in with the themes of your book; make sure your character has something interesting to say about the world they're in.
Also, try to make your POVs as diverse as possible. If you've already writing from the POV of a young, carefree male, try not to add another character's POV who is also a young, carefree male. Often, picking someone who is at odds with another POV can create contrast and conflict.
Select the right number of POVs
Many people ask, "what's the right amount of POVs in a story?" I've read "experts" say that it is three POVs, other "experts" say five POVs.
The truth is, is that it comes down to personal preference. Some readers will simply NOT read a book with multiple perspectives. You can't please every reader.
That being said, there is such a thing as too many POVs. Ensure the perspectives you include reappear regularly in the book. For newer writers, I would recommend adding no more than three POVs — simply because adding more can create more difficulties than what are already present when writing your first novel.
Once-off POVs
Many authors, such as George RR Martin and Brandon Sanderson, include prologue, epilogue or interlude character POVs.
Some readers like this because it adds to the overall world-building. Other readers find this distracting. There is no right answer. This choice comes down to personal preference.
If you're adding in a once-off POV, have the events connected to the main storyline, or contribute to the main themes of the book. Sometimes, introducing a once-off POV is a good way to set-up that character as a main POV in a subsequent book.