Look up addresses of the publishers you've identified that have a line or imprint suitable for your book. Obtain the name of the appropriate editor to submit to. If you submit to nobody, it will go to nobody and land in the slush pile graveyard. Get latest catalogs and submission guidelines. Some publishers have separate writer's guidelines for each category, others have just one Guideline sheet.
Some guidelines are now available via the Internet.
Write a sizzling query letter. This is your sales pitch, your door-opener. Less is more. If you have secured BIG NAME endorsements, Television or Radio Talk Show invitations, this is the time to mention them. Revise synopsis until it's perfect.