A script for what? A play, a TV programme, a film?
One suggestion is to try and find a book that actually includes exercises to help you actually get it down. I remember Graham Linehan recommending
this book, which is more of an exercise book that you can work through. Basically they asked loads of professional screenwriters to contribute one exercise to help people learn and then compiled them into a book. I haven't done much myself, but from what I've heard, just getting it down is the main thing, and then you can start developing it. The first stage would be a script outline though, where you basically outline what you want to happen in each scene. It can be useful as a beginner to have a template like the one from Blake Snyder's Save the Cat, which while formulaic, gets you to think about the purpose of each scene. As they say, you have to know the rules before you can consciously break the rules.
In terms of reading, you might actually be better off reading more actual scripts, and then analyse how the scripts you enjoy differ from the supposed formulas in the books you've read (nothing happens in Rocky for about 40 minutes, for example, despite all of these gurus insisting that your inciting incident needs to be within X pages). The other thing that might be useful is some sort of writing group, even if it's just other amateurs, so that you have motivation to get something down and people to give you feedback.
On a side note, Chris Morris was on Adam Buxton's podcast the other week and described scriptwriting guru Robert McKee as a snake oil salesman after him and Charlie Brooker went to one of his sessions and found out that he basically couldn't justify any of his points and got angry with anyone who questioned him.