Since a film is a story told in the dark, the most important aspect is the screenplay. You can have fantasitc camera work, but if the story is boring the film is boring. Every element is to tell the story in the best way possible, without distracting too much from it.
A screenplay is a story told with pictures. About a person, or persons, in a place, or places, doing his or her "thing."
It is s a series of events that occurs when a "sympathetic" character encounters a problem/complication and attempts to resolve it. Sympathetic character = someone you can relate to. This doesn't actually have to be someone you like or want to succeed.
Unlike a novel or short story, a screenplay focuses on describing the literal, visual aspects of the story, rather than on the internal thoughts of its characters. In screenwriting, the aim is to evoke those thoughts and emotions through subtext, action, and symbolism.
A few random ideas to think about:
Fiction is ordered chaos.
Less is more.
Show it, don't tell it. Instead of characters talking about doing something, show it.
Enter late, leave early.
The next 12 tutorials are all about screenplays. How to start, format, all about 3 dimensional characters, conflict, ect. While these are the first ones I have written, great screenplays really are that important and difficult to write. It may seem a lot of information, but in all actuality this is just the basics.
You have to write a clear and concise story that is not only interesting, but produces visuals in the mind of the reader. Not an easy task.
The only real suggestion I have is to read through them, let them soak in and then promply forget them. Let the ideas sit in your subconcious while you write, indead of fretting over every detail.