On the whole, screenplay format is pretty standardised, and thankfully screenwriters barely have to think about it thanks to the use of modern screenwriting software.
Some of the formatting controversies of the past have been dealt with and become canon: Avoid using parentheticals or transitions unless absolutely, vitally necessary. Simple enough. Two controversies remain though.
For once I’m not talking about the screenwriting software Fade In, but the necessity to begin every screenplay with FADE IN: and end it with FADE OUT. Certain guides will tell you it’s mandatory, some will tell you it’s tradition and you should just do it. Many newer to the industry will say it’s redundant and can be skipped, leaving the choice of fading, cutting etc. to the director like all transitions. There’s pretty much no consensus other than this: Keeping it will seemingly annoy nobody, while removing them could irk some. So we may as well use them, and some of their variations. A word of warning though: There should only ever be one of each in the screenplay.
I don’t refer to line-spacing, but the number of spaces after a full stop in a screenplay. After years of beautifully laid-out treatises, typographers finally convinced us all that putting two spaces after a full stop was redundant, as these days we have typefaces and word-processors that handle the kerning properly. The restrictions of mono-spaced typewriters were a thing of the past. Except, however, when writing a screenplay, where we use a mono-spaced Courier font, to facilitate standardised spacing, partly to assist in judging the minute per page pacing. Again, nobody is going to throw your script in the bin for only using a single space, but apparently it’s easier on the eye of a script reader to use two spaces. And these are the people who’ll make the first decision on whether to pass on your script.