A group I belong to once wrote a booklet called What's the Point of Point of View.
This series of tips will be about the two most commonly used ones. First and third person accounts of a story. This will start with First person.
In first person, the I's have it. In some ways this is the easiest viewpoint to write and it is also the hardest. First person is used when the story is to be told from a single person's point of view, most of the time. A favorite historical writer once wrote a book using first person hero and first person heroine.
When writing first person, only what the viewpoint character can see, hear, touch, taste, smell and think are possible. Unless the character can read minds he or she can't know what a person thinks or feels other than what they can discern through observation.
There are several problems that can be encountered while writing first person. The first is the constant use of I and varying the sentences can help here. Searching for ways to eliminate the use of I takes work. Another problem is tangents. The story can be forgotten while the character goes off on something that's not related to the story.
I speak from experience. I have a series of cozy mysteries begun in the first person. When I finished the second or third draft of the book I had a lot of words, but I had to go through and excise all the ones that didn't do one of three things, advance the plot, develop characters, or give vital information such as descriptions of places and clues or wild geese to fool the reader.
First person is very effective in mysteries, especially cozy ones. Another place I've seen it very effectively done is when the writer uses it in short segments to allow the villain to have a voice. Lately, I've read a number of romances done in first person and when reading the love scenes I feel very uncomfortable. I'm not sure why and for some people writing in first person comes easy. Maybe that's the reason.
Just remember when using first person, try to remember the story and rein in your character when they get carried off on some tangent or when an I pops up in nearly every sentence.