Sometimes I see scripts that introduce a lot of characters all at the same time. These tend to involve scenes that take place in restaurants or at parties early on in the story. It’s okay to add maybe two or three new characters in a single scene, but if you have any more than that, you’ll need a good reason why it’s important to introduce them all at once. The main problem, of course, is that the reader and the audience will have trouble remembering all those new people that you just threw at them in rapid succession. Think about what it’s like if you’re at a party and meet a bunch of new people all at once. Chances are you won’t remember all of their names unless you use a specific mnemonic technique to make it easier. That’s exactly what it’s like to see a bunch of new characters all at the same time in a script.
Since using a mnemonic device is a good way for people to remember names, you should provide your reader with ones that they can use to remember your characters’ names, whenever you think it will be helpful. Some people call this the “limp and eye patch” rule. For each new character that you introduce, give the reader a strong visual image that will help him remember who that character is. The scene in “Goodfellas” where Henry walks through the bar introducing characters is a good example of this. For most of the characters, he gives this kind of vivid description that makes the characters easy to remember: “Fat Andy,” “Freddy No Nose,” “Nicky Eyes,” “Jimmy Two Times.” You don’t need to do this with your main characters, but it’s always a good idea to make the other characters as memorable as possible.
In addition to giving your minor characters a useful mnemonic, it’s also a good idea to remind the reader who your characters are when you haven’t involved them in the script for a while. For instance, you could say “Johnny the bartender” or “Marissa from the park” or “Alfred’s cousin, Gwen.” If it’s been more than 15 pages or so since you’ve mentioned a minor character, just add a couple of words of description like that to make sure that the reader knows who you’re talking about. (Okay, “about whom you’re talking,” but does that really sound better? Really?) If a reader has to flip back through a script to figure out who one of your characters is, that’s not going to bode well for your script since the audience won’t have the luxury of rewinding the movie at the theater. I’m sure that technology is in the works but, until that magical day, we'll just have to keep writing clearly.