Develop a concept for your fantasy screenplay. You need to be able to write one sentence that describes who the hero of your story is and what he wants to accomplish throughout the story. Be as specific as you can as you develop your concept while still using just one sentence to describe the concept.
Develop characters for your screenplay. You need to write a page that describes what each character looks like, acts like and thinks like. The most important character is going to be the hero of your story, so it's a great idea to start with describing the hero. Your hero will need a goal, and she will need to face conflict along the way to make the journey interesting to the audience.
Create a timeline of events that you will use during your fantasy screenplay. This timeline will show your plot over time and put your series of events into a logical order. There should be a conflict that is central to your plot, and all events should be in relation to this conflict.
Break down your screenplay into three acts. The first act should be around 25 to 30 pages and should introduce your characters and establish the main plot. The second act should be around 50 to 60 pages and put your hero into conflict. The third act will be around 20 to 25 pages and contain the climax and resolution.
Begin writing your individual scenes that fall within each act. It's especially important in a fantasy screenplay to describe the scenery vividly as you write the dialogue for your characters.
Keep writing your screenplay, going back to change your individual scenes as needed. Keep looking forward as you write, being sure not to get discouraged and seeking help if you hit any roadblocks.