I came across this question on Quora:
“I have all these ideas in my head just waiting to be written. I have a broken plot line and can picture some of the scenes. I just can’t seem to start it. Every way I do it seems wrong. Should I reorganize my thoughts first? Am I looking at it the wrong way? What should I focus on when writing the first draft?”
There is no ONE right answer to this so here are some of my thoughts – Having written scripts (some even made into movies) the best place to start is 1) define the central conflict 2) write character studies for main characters 3) decide what in act 1, act 2, and act 3. The Avengers is a good example of the 3 act film (screenplay). Act 1 defined the central conflict to be resolved. Act 2 (most of a screenplay & the movie) is about the question: Can I (the protagonist or in this films case, a team of protagonists) find it within myself to do what needs doing to save the day or will I just fall apart? This is man vs himself. In act 3 of Avengers the unified team goes after the bad guys and come out on top. The meat of the story is always in act 2.
Visit http://www.writersstore.com.com and buy “Story Engineering: Mastering the 6 Core Competencies of Successful Writing” maybe it will help. Buy a copy of Final Draft 8 for writing. Rule #1-There is no one right way to do this. I have outlined, created beat sheets, on and on. Rule #2-Write the story first. Make it 1 page or 100. Even more (ugh). Shorter the better. Remember 1 script page is equal to 1 minute of running time. (90 page script is a 90 minute movie) Rule #3-Research and research and when your done research some more. Fiction or bio pic. For software I like Contour. Great for getting ideas down and not letting you forget key elements.
You will need a ONE SHEET (the movie in a page) and a log line (the movie in a couple of sentences) if it isn’t doable then the script won’t work. And last but not least REMEMBER Rule #4-The director will direct the film not you so leave out all the directorial comments and stick to key elements. Oh, and Rule #5-Write every day! Good luck.