Decide on the ideal market for your publication. If it's a travel book, then travel book stores are obviously the best option. A book about photography would be better in an art bookstore than in a large retailer.
Research the varieties of book distributors on the market. That can be done roughly over the Internet, asking a local bookstore which distributor they deal with, reading the backs of the labels of a similar publication in a store and seeing who distributed it, or going to a book expo.
Put together a pitch or press release for your publication. This is going to be your short and quick argument on why a distributor should carry your publication. A good pitch should be a succinct, effective argument that explains the financial, critical and intellectual promise of your publication.
Contact an employee of the distributor who deals with acquisitions and read him or her your pitch. Some of the larger distributors deal only with literary agents. If you do not know any agents or cannot get in contact with one, then start with a smaller distributor.
Work with the distributor to allow any prospective changes they may want in your book. Remember, they stand to make money off the book or magazine as well.