Writing screenplays is one of the easiest jobs you'll ever do; and one of the HARDEST. It's easy, because you get fired up by this fantastic idea that you know will be killer on the screen, and that enthusiasm makes you just jump right in and start typing.
And screenwriting's hard because you run out of that 'start up' energy often long before you get to those famous words - The End. That 'sticking point' is the exact spot where real writers show their mettle; or true grit. But they don't survive on pure grit alone; real writers have a whole arsenal of tricks up their sleeves. The most important tool they use is PLANNING.
Sounds kind of mundane, doesn't it? Planning - kind of like birth control. Can't we just 'be' in the moment and jump into this thing, honey? WE CAN.... and many do. But I don't any more, after many, many late nights spent staring at the computer screen and a script that I had loved six months before and now loathed because I couldn't seem to tinker away all it's flaws. Screenwriting has taught me patience and the ability to control that 'start up' enthusiasm.
I urge all of my students to create a number of tools while the novelty of their movie idea still has them panting to write. It's then, when you're desperate to get at your computer and really type, that you really should rein in your excitement about writing and answer some really important questions.
Like: Who's your main character? What is it they want? What gets in the way of them acquiring it or achieving their goal? How badly do they want what they seek? Who are the important people in their life and how do those relationships complicate their quest? Take these questions and create a logline, a 5 page treatment and a working title and you're on your way. Throw in the opening and closing scenes for each of the 3 acts and you should be ready for nearly any thing!
Once you've got this material firmly in hand, you're ready to unleash the creative hounds and hit the keyboard running. With planning, and careful conservation of that 'start up' energy you may find yourself at 'The End' before you know it!
I hope this helps. I wish you luck with your screenplay. And let me know when you finish it; I'd love to read your work!