The characters that you create for your screenplay are just as important as the actual story that you want to tell through them. Your characters will make or break your story. If your characters are boring, one dimensional and unidentifiable then your overall story suffers. You get people to care about your story through the characters.
It is very important to create multi-dimensional characters that your audience can relate to and want to see succeed in achieving their goal. Writers have to really get to know their characters before starting the script. One way to avoid creating characters that we have all seen before is to create a detailed biography. You should know everything about their background such as their family history, education, accomplishments, and deepest regrets. It is important to portray them as well-round, complex beings.
Take a look at Harry Potter, the young wizard protagonist of J.K. Rowlings amazingly successful book series. Harry Potter is a very multi-dimensional character. We learn early on that he is a half-blood prince with a very sad past. He is a bit of a loner that has been taking care of himself since he was very young. Harry Potter is a gifted wizard that is in constant danger. And he evolves into an even more interesting and complex character during his attendance at the Hogwarts School of Witchcraft and Wizardry.
Take the time to really consider the protagonist of your story. Give your characters traits that are not cardboard cut outs of other characters we have seen time and time again in other stories. Think about the people that you know or have read about, you can make a compilation of different personalities to create your characters.
The next time you go to the movies, really study the characters. The Harry Potter series is a good place to start. It encompasses a great mix of unusual yet interesting characters.