How does the Standard Screenplay Format help the writer write?

First and foremost, the Standard Screenplay Format is designed to produce a screenplay that reads at a page per minute. A reader should be able to easily read the screenplay within two hours. If it takes longer, the writer has failed. It is designed to be easy on the eye, simple to scan lines. As the reader becomes interested in the story and characters, the writing should almost disappear and be replaced by the reader's imagination.

Where do we start?

With a little fact. Rules can be broken. But you must follow the rules to break them. Ignoring the rules is just poor craft. That is why breaking the rules has such power. Like derailing the audience, you set your reader up and then shock them when you break the rules. It's a great way of getting an effect. Shock them too much and it loses its effect. So on with the rules.