Every book should have a clearly dominant primary viewpoint character and it will be your protagonist.
Your novel should be told from a viewpoint inside the action. If the description is colored by the viewpoint of the protagonist who is doing the noticing, it becomes part of character definition and part of the action.
Your protagonist is the one who has the most at risk, the one who will be changed most by the story. The protagonist is also the one whose struggle toward a goal is the energy driving the story. They must solve the problems of the story, and they will be actively involved in the plot.
How do you establish viewpoint?
You establish the viewpoint of the protagonist by forcing your own imagination to see everything from the protagonist’s viewpoint.
Here, from my book Revenge in Reno, is how you let readers know who the viewpoint character is.
Veronica walked up the wheelchair ramp to her neighbor's porch and knocked on the aluminum door. She gazed at the Truckee River flowing through the center of downtown Reno. The drought had left the river much lower than usual and it saddened her.
Once I wrote, “she gazed at,” readers know all that follows is what Veronica sees, knows or thinks.
A beginning writer of fiction may write stuff, which has no viewpoint, like this:
"Veronica stood on the hill. Down below, a crowd was...."
"It was quiet. Then a sound..."
"Something crawled across Veronica's hand..."
An experienced novelist will take the situations and rewrite them to make it clear where the viewpoint lies.
"Looking down the hillside, Veronica saw the crowd..."
"In the dark, quiet room, Veronica heard a sound..."
"Veronica felt something crawl across her hand..."
How else do we show viewpoint? By telling things, only the viewpoint character could know.
• Sense impressions, like the protagonist, hearing a sound and feeling something crawl across her hand.
• Thoughts, like "Veronica wondered if Chuck was stupid all the time or only in front of women."
• Emotions, like "Veronica, felt as cold and isolated as an only child."
• Intentions, like "Veronica, had to find out where the killer had left the postcard; it was the only clue usable in court."
The viewpoint character cannot see their own face. If someone is sneaking up behind them, they can't see the person. The protagonist cannot know what is going on inside anyone else's mind. The best they can do is guess. Which, by the way, is the way we do it in real life.
Consider this. If you and I talk, there is no way for you to read my mind. Only I know what I'm thinking. You may say, "I can look at a person and know exactly what she is feeling." Not true. You can only guess. When you see a woman crying, you can only observe the superficial clues and draw a conclusion about her emotional state. You do not know. The only possible way readers can know a character’s thoughts are if we are in that character’s viewpoint.