Write a killer script. You need an amazing script. Make sure it is in proper industry standard format. This is important, or a reader may simply trash the script without reading it. You should also write a log line. A log line is one to two sentences that describe your film. Think of the short descriptions in the newspaper for the films in a theater. Those are log lines. It should simply be a stunning summary of your film.
Write a one page synopsis. A synopsis is a brief description of what your film is about. It includes the basics of what happens. It should be 3 or 4 paragraphs long.
Copyright your work, and register it with the guild as well. These are two separate entities, but both processes are equally important. Make sure to do both to ensure the safety of your work. You worked hard, and your work should be honored with protection.
Find a literary agent who is currently accepting new clients. You can find these lists and postings online. The Writer's Guild of America hosts a comprehensive list of professional agents.
Send query letters to as many agents as possible. See who responds and wants to see your work. It's alright to submit the work to many at this stage.
Respond immediately to agents that express interest in your query. Try to set up a meeting, and send your full script the same day that you receive the acceptance.
Sign with an agent if possible. If he is hesitant or decides not to hire you, ask if he is alright with having his name attached to you on a trial basis .Being able to use your agent's name on a query to a studio can make the difference between having a script read...or having it tossed in the trash.
Research which studios are making films in the genre that you write.
Submit the script with your agent's name, or have your agent submit the script for you. It's best to have the agent do all submissions if they are taking you on. Clear any submission with your agent before sending it out, especially if your are using his name.