Give a carpenter a truckload of tools and a bunch of wood; he’ll build something. But hand him structural blueprints as well, and the end result will be amazing.
Screenwriters work the same way, and the outline is our skeleton. Personally, I enjoy writing a detailed framework – often 20 single-spaced pages brimming with snippets of dialogue – because I find that when it’s time to actually sit down and write the script, I’m able to move through the pages at Formula-1 speed.
There is, of course, no magic recipe as to how much you should include in an outline, but the most rudimentary plan should contain at least the following five elements: (1) Who’s the protagonist and what’s her goal, (2) Who are the supporting cast and what do they want, (3) What are the five major plot points, (4) What is the order of events, sequences, and act divisions, (5) What scenes do you think will help tell the story?