1. Make a great idea! It should be about a protagonist who embarks on the quest. That may be a guy (protagonist) who saves our planet from an incoming asteroid (quest). It could be in regards to a woman who may have to re-enter the work-force after you have divorced. It could be with regards to a number of mountain-climbers who climb Mount Everest.
2. Find screenwriting software that you want. You will find top-notch screen-writing programs on the market at almost any price-point. If you fail to spare the amount of money, there’s also really good free options available.
3. Make your protagonist or main-character. Anyone the movie’s going to be about. Provide him reveal backstory.
4. Give your protagonist a character-flaw or internal-conflict. Maybe he’s a drunk. Maybe he’s a racist. Maybe he treats his children poorly. It may be anything. So long since this character-flaw is preventing your protagonist from achieving their goal.
5. Create fully fleshed-out supporting-characters. Some can be trying to strengthen your protagonist, some may be working against him. Provide them with backstories and names.
6. Convert your idea onto a 3 act strucutre. screenplay format should choose to attempt their quest at the conclusion of the first act (the 1st turning-point). There should be a false-victory or defeat around the mid-point. The stakes should rise dramatically at the end of the 2nd act (2nd turning point), and also the quest needs to be decided in the climax.
7. While using story-structure you just created, create your entire scenes. Don’t be concerned about writing the scenes themselves, like the action or dialogue, just take note of a short sentence or two over a cue card in what needs to take place in that scene.
8. You should have a pile of cue cards, listing your entire scenes – along with what you need to do in each one. Now is the time for a few minor re-organizing, should you desire. Just re-arrange the cue cards!
9. Once you have your storyline, it’s time to start writing your screenplay! Go ahead and take first cue card off of the pile and jot it down! You’ll need to flesh it, of course. You will have to add dialogue and action.
10. Congratulations, you’re now a screenwriter! You just wrote your first Hollywood-style screenplay! Now you must to transmit it to film-producers and movie studios!
For more info about how to write a screenplay you can check this useful resource.