Polish your script. Cut unnecessary scenes and characters, embellish your fictional world, round out your characters.In short, make sure your script has something special to say or else it does not stand a chance.
Write a one-page synopsis of the script to send to agencies. It can be hard and frustrating trying to condense your script into a single page, but agencies receive thousands of submissions each day. They will appreciate a short, easily readable synopsis.
Write a query letter. This should contain a logline and a brief personal resume and be no more than three-quarters of a page long.
A logline is a one to two sentences meant to capture the agents' attention and sell your script. The more provocative the better. Instead of "A woman confronts her past when her illegitimate daughter shows up after twenty years," write "A minister's wife confronts her long-buried past when her illegitimate daughter shows up after twenty years." Focus on character, want, and conflict contained in the script when writing your logline.
Find a list of reputable agencies, such as the lists provided by the Writers' Guild of America.
Call as many of the agencies as you can and ask for the names of any junior agents accepting new clients. It is probable they will say "no," but if you get a name, write it down. If possible, speak with the person and try to sell your script over the phone.
Send your query letter, addressed to the junior agents, to as many agencies as possible. Addressing it to a junior agent insures it will end up on someone's desk and will not be thrown away by a secretary.