In order to sell your idea for a magazine to a publisher, distributor, wholesaler or retailer, you need to have a great idea, developed into a convincing pitch, and supported with a dummy or other concrete demonstration of what the magazine will look and feel like.
In the clip, David Howell explains that the pitch is essential, so any potential partner knows what they are going to get if they work with you.
Back your idea up; demonstrate a gap in the market and have the research to prove that it exists.
Look at the sections of Masterclass 12 at www.multimedia-journalism.co.uk on creating a business for much more on this topic. You'll also find David Howell's full Magazine Publishing Masterclass at http://www.multimedia-journalism.co.uk/node/749