Omtech,
Your script will have to conform to the traditional Screenplay or Television (long & short form) style scripts. If it's not properly formatted, it will be obvious and the majority of producers will pass on it early no matter how well written. Formatting should not be a problem as there are many good software programs like Movie Magic and Final Draft that will automatically format your script for you. Also, there are tons of sites and info on the web on how to properly format a script.
The toughest part about scriptwriting isn't formatting, it's translating a story into a script compelling enough to make the reader (i.e. potential investor, producer, director, actor) want to put forth the effort to make it into a film. We've all seen movies and TV shows we didn't like if not outright hated. But, those as well as the one's we loved were all successful because they all got made!
So except for the formatting, there aren't any hard and fast rules about writing scripts. There are some 'guidelines' though.
Be consistent. Maintain a 'believable flow' with your characters and events. Nothing makes a movie suck more than having those 'WTH' did that come from? moments in it.
Don't rip off other writers. There's a huge difference between an 'homage' and straight up theft. Few scriptwriters in the last 50 years can not say they haven't taken influence from other films. You can however parody (make fun of) a scene from another movie or use a similar situation in your own script. Better make sure it's obvious that's what you are doing lest you run into copyright infringement at max and your audience calling you a 'rip off artist.'
Write your story your way. The scripts that always stand out were written from the creative perspective of the writer. That may sound vague but it works.
Oh, and don't be afraid to 'kill your baby.' Be in love with the script you're writing but don't get attached to any specific part of it. By doing that you'll be more likely to make clearer editorial judgements. Parts of the script may not flow well, make sense or just have holes in the plot that semi-trucks could drive through in tandem. When that happens, you'll either have to rewrite or cut out that portion altogether. Also, it prepares you for the pain when changes are made during production and post-production. Rarely does a script go from writer to theater unchanged.
