I would never begin writing without a plan. Why? Because the plan will change anyway. Once you put your characters in a room together, their interaction takes on a life of its own and it may steer the characters differently. That's okay, but if you don't have a map to begin with, metaphorically speaking, you're going to get lost. Your outline is your map...

Here's how I make an outline. I break the script down into scenes, and for each scene, I write the pertinent things that must happen. For instance, in Scene 1 you could write, "introduction of main characters problem," and as you refine your outline, you get more specific.

You'll want to accomplish a few things. #1 is always story, the scene must push the story forward #2 Character development- so we are learning something about our character that will come into play later. For instance, in Indiana Jones, as he's escaping from an island of savages, there's a snake in the plane to which he exclaims, "I hate snakes!" This sets up the scene later where there are snakes everywhere. Think in terms of "set up" and "pay off" when you write character development.

Sometimes you'll have a hilarious scene that accomplishes neither. Some people will say cut it, I say leave it. As long as you are moving the story forward in your other scenes, my philosophy is, this is a creative endeavor, so don't get too bogged down in following rules. But! Do! Follow! Structural! Rules! Even though my exclamation marks contradict my statement, you get the point.

In each scene, have a beginning, a middle and an end. Start the scene at the latest point in the scene and end it at the earliest point. Why? People get bored. Starting a scene with, "Hi" is shit! They met, they greeted, we get it. Start with, "So, I'm pregnant." Get it?  Good, now tell me a story by putting together an outline. Then you've earned the right to begin really writing.