When creating characters, a common mistake many new writers make is to create characters that are too similar to one another. I made that mistake countless times myself.
If the characters we have created are too similar to one another, they will act in the same way, will wear identical clothes, or will order the same place in the same place. Your reader will quickly get confused, often too confused to carry on reading your screenplay.
In your, the writer’s, mind you might be seeing your characters very differently than you describe them on paper. However, your reader will not see what is in your mind. For the reader to know what you see, you need to include the differences between your characters in your script. It can be anything from the way they wear their hair to the type of tea they drink in the morning. If your characters are too similar, you will lose your reader pretty quickly, and your screenplay will end up in a bin; no reader wants to go back a few pages to re-check who Stacey is, and why they thought she was Anna.
What I like to do, when I develop my characters, and I’m not the only writer who does that, is to give each of my characters something unique that only they do or have. For instance: Brad Pitt’s character in Ocean’s franchise – Rusty – always eats something; it’s his thing. Ron Weasley from Harry Potter movies is a bit clumsy, and things mostly don’t go his way. The audience and readers will quickly pick up on that, and every time they see Ron, they will already have a mental image of him. This is what you want your readers to have, mental images of each of your characters.
While developing your characters, make sure they differ from one another. Give each one of them some very unique traits, specific only to them, such as eating, being clumsy, blurring things out without thinking much, being uptight, speaking with an unusual accent, or trying to hide their original accent, wearing very out of place clothes etc. (the sky is the limit). If you want to see a fantastic range of characters, I suggest watching The Office (the US version). See how each of those characters is different with their own unique traits and quirks.
Don’t lose your readers by blending all your characters into one indistinguishable persona. Make your characters stand out from one another, give each one of them something very individual that would show your readers something about them that not only completes the character but also makes them more human.
While you are here, you might also be interested in Creative Distribution.