Screenwriting is different from other literary forms. The script is essentially a "blueprint" that will guide the other filmmakers through the production of the film. Often, the final film will differ from what was on the page. These differences can be as small as a few simple dialogue changes, or as large as a complete change in tone, direction, and intent. Accepting this process is key to being a screenwriter who not only writes well, but will work well with the other people involved in the film's production.
In addition to being the blueprint for the film, the script also serves as a way to get that film made in the first place. Based on the strength of your screenplay, budget, talent, and enthusiasm will fall into place. It is the strength of the story that can secure financing and production talent. It's not innovative and thrilling setpieces or even a smattering of really great scenes peppered throughout your script, but a cohesive, intriguing story that holds the reader's (and eventually the viewer's) attention from beginning to end. This is such a basic concept, and yet one that seems utterly lost on some screenwriters, even those already established in Hollywood. Every script should be written in the industry format. The industry's script format help readers to understand how long the movie is going to be. The screen writer has to be creative and original and also to be flexible with the script and to adapt it to the budget of the film.