You may already know this, but with a non-fiction, how-to type of book, most editors require a proposal first. They're going to want to know your "platform," i.e., your qualifications for writing this particular kind of book and what you've already done to build an awareness of yourself in that particular niche.
Publishing these days is increasingly like the rest of the entertainment industry...who you are will do more to sell your book to a publishing company than what you're writing about.
