I was recently commissioned to write my first screenplay. I was given a synopsis and certain characters and asked to write around it. Just finished the first draft and sent it in. Quite pleased with it. I was worried for a bit, but once I got past the halfway mark, the story began to take over and really flow. It's funny how the words just come when you know where you're going.
I've written for the theatre all my life, and it's quite freeing in some ways to be able to essentially follow someone when they leave the stage. I've always said the versatility of theatre is great, because you can have someone stand in a blackbox and say "I'm on the moon", and so they are. But actually writing that someone goes to the moon is another thing entirely when it comes to film, because then someone will have to build a moon set and probably a space suit; probably I'm quite lucky that my first assignment was for an animated feature, it takes some of the onus off me to make things affordable.