I’ve combined these two points into one since they should be fairly obvious to everyone who writes screenplays. However, I feel it’s important to mention them since I still see so many scripts that have nonstandard formatting and that are riddled with spelling and grammar mistakes.
The first thing that I think when I see scripts like this is that the person isn’t serious about being a professional writer. Harsh, right? Every screenwriting application and word processing software package comes with a spell checker, so please use it before sending your script to anyone. One reason for this is because a spec script is more likely to get you a writing job than a sale, so you need to demonstrate that you are a good writer in every respect.
Also, if you haven’t taken the time to learn proper screenplay formatting, then why would anyone think that you are committed to being a screenwriter? Screenwriting software is available for free online at celtx.com or as a Microsoft Word template, so there’s no excuse not to format your script correctly. There are also numerous guides on screenwriting structure, such as David Trottier’s indispensible “Screenwriter’s Bible” (and his web site at keepwriting.com), so take advantage of these available resources to make sure that your script is perfectly formatted before submitting it to anyone.
Note that if there are some formatting issues in particularly tricky parts of your script, such as a complicated action sequence or a series of shots, those won’t count against you as much as simple mistakes, such as noticeably incorrect margins or indentations. As long as you are clear and the reader will have no trouble understanding the action, then you’ll be fine.