Soliciting distribution is not a science, and every business you approach does it somewhat differently.
As a primer, you'll need:
-full-length screener
-synopsis
-copyright/clearances/releases from all people, places and things on camera
-asking price
Only solicit those companies that sell similar/like product...

Most distributors will want to see the finished product before finalising a deal (although you may be able to start the discussions with something less). It's unusal for any distributor to finalise on a trailer only, as of all people, distributors know the most how easy it is to misrepresent a film in a trailer.

Ben C.

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filmmaking.net
(Incorporating the Internet Filmmaker's FAQ)

Please note the opinions expressed here are those of the author only and do not constitute legal advice. The author cannot accept and liability whatsoever for inaccurate or outdated information contained within.
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All great advice here.

But you'll never get a better answer than directly from the distributor. Call the ones you think will be interested in your show and ask them what they are looking for.

I've sold movies based on a screening in a theater - even for direct-to-video projects. Hire a theater, invite 200 people and hold 10 seats for the 100 distributors you invite. Nothing better than a screening with people who will react! Beats looking at a trailer or even the entire movie in your office with the phone ringing.

Sometimes it takes three or four screenings before even four or five will show up. I just did one on May 31 got two to show up. And one sales agent (producers rep). The screening created a buzz. We have another one set for Aug 1 and already it's easier to get distributors to rsvp.

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The aim of an argument or discussion should not be victory, but progress.
Joseph Joubert, essayist (1754-1824)