I got an idea for a screenplay based on the album In Absentia by Porcupine Tree. Not looking to actually get it made into a movie, I just think it would be a fun project (could it count as a novel for national novel writing month?). So I'm asking: have any of you written screenplays before? Do you have any tips to make the process easier/more streamlined?

I think to avoid writing yourself into a corner, it might be good to write the beginning and the end first, and then think about ways to connect the two.

If your budget can afford the expenditure look into the screenwriting software that is available, some professional grade, some not so much . . . choose your poison =)

Also there are instructional books available on-line (search Amazon for "Screenwriting books / software") You can also find complete bundles of instructional books about screenwriting . . at some ah . . ah . . sites.

Edit: I should add some of the software programs are free. Using software designed for screenwriting may eliminate some of the learning curve through established formatting.

Knowing jack-shit about screenwriting... be mindful of the dialogue. I've noticed that what works in stories and novels is absolutely inadequate for the acting.

I've read that it's good to finish your first draft completely before you start revising. Just put everything you can down on paper, then work on consolidating and editing it. Good luck!