A proper noun is a title given to a specific item or entity in order to distinguish that item from others of the same class. Essentially, a proper noun is a name. (There is a whole, deep linguistics debate about the exact difference between proper nouns and proper names, but we don’t need to go into that. For our purposes, the simplified definition proper noun = name is adequate.)
So, for instance, Canada is a proper noun that is used to distinguish one country from all others. To Kill a Mockingbird is a proper noun that identifies a single book out of all others. If you were describing a group of girls, you could distinguish them by their names; Elizabeth, Meghan, and Catherine, for instance—all proper nouns.
Every story contains proper nouns: names of characters or places, titles of companies or ships or official positions, or even just names of ideas and theories. Some will have more than others, of course; the number will depend on the size and needs of the story. A short story that takes place in one location with only two characters will need far fewer pronouns than a trilogy of novels that visits a dozen locations with fifty characters.
The important thing to remember about proper nouns is this: they are difficult to remember. The more you give to your reader at once, the more confusing the story will become. This doesn’t mean you can’t have a story full of all sorts of interesting pronouns—it just means that you need to learn to pace yourself. Arrange your story so that you can start with just a few new pronouns; once the reader has those down, you can give them a few more, and then a few more.
Here are some things to keep in mind regarding pronouns:
Avoid using pronouns where a common noun will do: If the main character of your novel will only speak with Brian Elmson the security guard once, then Brian probably doesn’t need a name. He can simply be “the security guard.” If your character loves guns, it might be good to describe their handgun as a “Glock 30SF”; otherwise, you can just call it a handgun.
This is a particular problem in fantasy and science fiction, in which authors often have to come up with numerous pronouns to describe the various non-existent magics, technologies, and alien races that they’ve created. Don’t add any more then you have to—for instance, don’t call your character’s knife a Dalkirk when it could just be a dagger.
Common names are easier to remember than unfamiliar names: Again, this tends to be a problem in fantasy and science fiction, but it is not limited to those genres. If you’re writing in English, most readers will remember “Matt Davidson” and “Tyler Smith” more easily than “Yeon Gaesomun” or “Vyachislav Dimitrovitch.” That doesn’t mean all of your characters should have common English names—it just means that if your readers are already trying to remember “Yeon” and “Vyachislav,” it might be a good idea to name the next character “Matt” to give your readers a break.
Short, easily-pronounced names are easier to remember than long, tongue-twisting names: Even if your reader is not reading out loud, they’ll still have an easier time if they can hear the word in their head. So if you’ve got a Russian character, it might be a better idea to name him “Dima” than “Vyachislav.”
First letters of pronouns can be used to help readers remember: If you have several characters whose names all start with the same letter, it will be harder for the reader to keep track of them. Sean, Saladin, and Soo-mi are going to be harder to keep separate than Mike, Saladin, and Bo-yeon.
When creating new terms, incorporating familiar words can help your reader remember what the new term refers to: When Brandon Sanderson put magical swords into his Stormlight Archive series, he called them “Shardblades.” He could have called them “Trevinoagiki” or some other completely-made-up term, but it would have been harder to remember. Even if the reader forgets how Shardblades work, they’ll never forget that they’re swords, because the word “blade” is right there in the name.
This can also be used in non-fantasy works. Say your story takes place in the fictional town of Oakdell and the fictional city of Davis. If readers are having trouble remembering which place is the town and which is the city, just change the name of Davis to “Davis City.” Bam. Problem solved.