Movie screenplays follow some standard rules.  A full-length screenplay will be from 100 to 120 pages long with typically three acts:
•    Introduction – about 30 pages, which introduces the story
•    Body – about 60 pages, which is the main part of the story
•    End – about 20-30 pages, which includes the climax of the story
There are about 50-70 scenes in a screenplay.  Each scene will have a setting, where the scene takes place, a time, and something that happens that moves the story forward.

There are 6 stages with 5 key turning points in a screenplay:
•    Stage 1 – about 10 percent of the screenplay, the opening, which draws your watcher into the story and reveals your characters’ lives
•    Turning Point 1 – about 10 percent into the screenplay, where your main character is presented with an opportunity which will start him/her on a journey
•    Stage 2 – about 15 percent of the story, where your main character reacts to the new situation that has arisen from the opportunity
•    Turning Point 2 – at the 25 percent point in the screenplay, where your main character’s original reaction to the opportunity turns into a specific goal with a clearly defined finish
•    Stage 3 – about 25 percent of the screenplay, where your main character’s plan seems to be working; although, there will be conflicts and obstacles
•    Turning Point 3 – at the mid-point of the moving, where your main character must be totally committed to achieving the goal
•    Stage 4 – about 25 percent of the screenplay, where there are complications to achieving the goal and it becomes harder to move forward
•    Turning Point 4 – at the 75 percent point in the screenplay, where something happens that makes it seem as if achieving the goal is impossible
•    Stage 5 – your main character must push forward against all odds and the seeming impossibility of achieving the goal; everything is working against the main character
•    Turning Point 5 – at the 90-99 percent point in the screenplay, known as the Climax, where your main character faces the biggest hurdle of the movie, must determine his/her own fate, and the motivation must be resolved
•    Stage 6 – your main character’s new life is glimpsed

See http://www.creative-writing-now.com/screenplay-structure.html and
http://www.storymastery.com/story/screenplay-structure-five-key-turning-points-successful-scripts/ and
Alexandra Sokoloff’s blog: http://www.screenwritingtricks.com/