Basics of Viewpoint
The best way to choose viewpoint is to ask yourself whose story or scene it is. Once you know who the story is about it’s safe to assume that most of the story will be told from that character’s viewpoint, either in first person “I” narrator, or third person “She or he” narrator.
There are several kinds of viewpoint. "First Person" is written with an "I" narrator, as if the story happened to you. "Third Person" limited, is written in third person, but limited to a single point of view. This is the viewpoint chosen for most short stories. Also most girl-in-danger stories are written in first person limited, while Harlequin and most genre romances are written in third person limited. In either case “limited” means limited only to the main character’s viewpoint. The reader cannot know anything the main character doesn’t see, think, or feel.
The reader should see through the main character's eyes, feel with the main character's heart, and think with the main character's brain.
One way to get emotion across for a character, when we're in another character's viewpoint, is to use body language to express the other character’s inner feelings. Describing body language the main character sees will get the other character’s emotions across to the reader, whether the observing character understands them or not. Remember the classic romance ploy where the heroine thinks the hero is mad because his teeth are clenched and the inevitable muscle in his jaw is jerking, but the reader knows it’s only because he’s in the throes of desire. We all read body language all the time. It does no good for someone to tell us, "I'm not upset at all," if their face is red, and their arms are crossed firmly on their chest, while one foot taps the floor.
In some third person stories, viewpoint can change from one character to another at scene breaks or chapter breaks, but it should not jump unintentionally from one character's head into another. Many well-published writers ignore this rule, but if there's a slip, reviewers will always notice...