Rum and a blank page make for a great night.
I've been able to write since third grade and my degree is in English. That said, having the ability to write - even write crap - is something that many do not posses. If you know your characters, you should be able to put them into a scene and the actions / emotions should come quickly. Dialogue will likely come slower and if you don't have extensive experience in really listening or understanding people or how every single piece of dialogue has to move the story, then just write whatever works and come back to refine it.
One last thing about Save the Cat. As I mentioned, I've been writing poetry and short stories and about film for a long time. I'd had ideas for scripts in my head and even wrote a 60 pager. Then I read Save the Cat. Then I created a board. Then I wrote a complete 90 page script in 4 days. I just finished Richard Walters Essentials of Screenwriting and even read the Bible - Syd Field... but NOTHING will help you finish a screenplay better than Save the Cat. In fact, I read it (or at least most of it) every time I start a script and have been able to get a full draft done in a week.