A lot of people have thought about how to plot a film script, but many simply don't have the basic down yet that they need to tell a good story. A movie worth watching will always tell a good story. Good stories are told using some type of structure. In the world of cinema, as well as most novels, simply utilize a 3 act structure in which to tell their story. In the first act, you get the audience hooked with an exciting premise or idea. The second act is used to introduce conflict and get the good guys of the story into some trouble with an antagonist. The third and final act is for the climax of the story and where things come to a close.
If you want to know how to plot a film script correctly and actually have it get made into a movie, then having a good act one is very crucial. This is usually the part that producers will often read to decide if they are interested or not. If they read the first 25 pages, which is the typically length for a beginning act, and are not hooked yet, they are not going to bother turning your story into a film.
Act two is usually where the meat of your story will take place. After setting up the place and introducing the characters in act one, now it is time to put them in action. The most common plot device in movie making is a conflict between good and evil. Think of your favorite movie ever and it likely has a plot that has a good guy and bad guy facing off. It is important that you do not peak with your story during the conflict phase, as it will make audiences not interested in seeing the rest of the film. Knowing how to plot a film script is a learning process and although many have tried, many have also failed to get their scripts made into movies. And it is a pretty good bet, these scripts failed with their second acts.
The last piece of advice on how to plot a film script involves the third and final act of the story. This is commonly where the good guy overcomes the odds and prevails against the evil doer, although some movies try to be different and don't always close with a happy ending. Some films even leave their stories left open ended for the audience to decide themselves how it ended.