This article from MovieBytes.com gives some simple, practical advice for how not to give away your inexperience in the first few pages of your writing, the pages that every reader is going to judge you on and possibly not read past.
Don’t Worry About Writing Perfectly, Just Write!
This article from MovieBytes (a great resource for information about screenwriting contests) has some solid tips about how to improve your screenwriting, but this tip is the one that stood out to me most.
Finding Your Main Character’s Arc
James Hull has written a great article on Screenplay.com about how to figure out your main character's arc.
3 Tips for Getting Your Script to the Studio Level
Here's another great article from Michael Ferris.
10 Writing Tips from the Great Billy Wilder
Scott Myers of GoIntotheStory.com recently posted this list of ten writing tips passed down by the amazing Billy Wilder. Wilder was the scribe behind such classics as Some Like it Hot, The Apartment, The Seven Year Itch, Sabrina, and Double Indemnity, to name a few.