The biggest thing I tell new writers is to watch films, not for enjoyment, but to study them as if you were reverse engineering them.
Rent a movie that you (and others) consider to be well made. Any of the AFI top 100 would be good, or if you love or want to write a particular genre (horror, for example), rent a favorite.
While you watch it, have a pad and paper at the ready and make notes and observations of things. I used to plot graphs, write out each scene heading and how long each scene was, all sorts of stuff. I got knee deep into the film and got my hands dirty.
Ask questions.
How long does it take before you know what the movie is about?
When is the main character (hero) introduced-- the villain?
At what point does your hero realize he/she needs to do something?
When does the hero confront the villain and win?
How long after the win does the film go on (epilogue)?
If the thing that makes the hero win, hinted at or shown earlier and if so, when?
At what time intervals does the conflict or action rise?
(you'll find ten minutes is a common rule for any action based film, that's because in the old days a reel was ten minutes and they always wanted to end the real on a conflicting scene.)
This is just a short example. Write everything down you notice, no matter how small. Look at the pacing, the characters, leave no stone unturned. Write out some of the dialog or try and write the action in a scene, visually.
Now. Once you have done this, do it again with other films. Start looking for common things in different scripts, as those are the rules that all stories follow.
Sure, you should read the books, learn everything you can, but after.
I find it is much more rewarding (and easier to understand and remember theory in the long run) to deconstruct a film on your own first, then read the experts theories and see how close you were.
As for reading scripts, that too is valuable but again I would do so after I tried to see the script in my head first, because a good script doesn't make a good film, but a good film is made despite of its script's quality. With the above example of trying to write the action, looking at what you wrote and then the script, helps better understand how and how much to write.
That's it. It helped me and hope it does for you. I understand that not everyone can do it this way and again, this does not take the place of learning from classes, books, mentors and articles, but can be a good supplement or a jumping off point for those trying screenwriting out.