I have noticed this issue with seasoned and novice writers alike: a tendency to not only confuse the reader with changing character names and designations, but to use too many characters when it’s not necessary.
When you introduce characters, it’s okay to use their full names, but at some point you should try to settle on one name by which to refer to them. Otherwise your reader will be confused and might have to page back to the previous pages to hunt for who it is. This is not something you want your readers to have to do. I know that as a reader myself, I certainly don’t want to do it.
When you mention a character for a second time, and it’s been a while since the first time or the last time, give the reader some cue, like, “John, ever the nutty professor, joined them.” –assuming of course that John is a professor, and has been known to be nutty.
This caveat about character names and clues should be used with even more attention when you have more characters, as it becomes harder and harder for your reader to keep them clear in her mind. Some books do seem to require quite a few characters to tell the story, however. My first few novels had only two to four characters and the rest were peripheral or nameless (i.e., the “waitress”). –a definite indication of my greenness as a writer back then. Probably wise, though, to start those projects with only a few main characters, until I learned how to handle them better, and with more discernment. But I have come to recognize that more complicated plots require more characters, (not always, but usually), and likewise, more characters can help you create that sort of plot. Now, this is from my viewpoint of being an organic type of writer. I don’t plot out all my books down to the last detail. I feel that sucks most of the joy right out of it. So, keeping this in mind, that organic process tends to take root when you have different characters playing off each other. Sometimes the solution for being stuck in where your story is going, can be solved by some interesting juxtaposition in two or more characters, or by just allowing them to converse, until something pops up that offers you a solution.
In my novel, Achilles Forjan, I think there were about 33 characters, even though some were tertiary, and some were talked about, but no longer present in the story–they were victims of a killer. But all those characters were necessary to the plot, and I was careful to remind my reader in subtle ways, who they were when they were out of the picture for a while.
Another method I used to great success in Baggage, was to try to go to a different character in each chapter until I established them all, and then allow them to merge in chapters as their relationships intertwined. I learned this little trick from one of my favorite authors, Dean Koontz. (see blog entry on the Koontz Dangle).
No matter how you handle the characters in your books, just be certain that they are there for a tangible reason, and it’s clear which one is in the scene, and in relation to what other character or situation. No need to confuse things for the reader.