Write a logline, a one-page synopsis and a brief treatment for your script. A logline is a short, one- to two-sentence description of your story similar to the description in the newspaper for films in the theaters. A synopsis is a summary of your story. A treatment is an expanded summary of your story, which includes specific details and more information highlighting the key points of the script.
Obtain a copy of the Writer's Guide To Hollywood Producers or similar directory. These guides list all numerous producers, their contact information, what kind of scripts they're looking for and information on how to submit work to them.
Go through the guide and make a list of all the producers who happen to be looking for scripts like yours (such as dramas, family comedies, low-budget horror).
Follow the instructions of each producer on how and what to submit. Some producers ask you to send an email while others want a hard copy of a query letter and synopsis only. Every producer wants a query letter, which is a short cover letter introducing yourself, and the logline of your script.
Send out your queries and wait for responses. If a producer is interested, he may request a treatment or the full script for review.