Contacting potential agents
I have three nonfiction books, two are out, one will be officially released tomorrow, March 1, 2005.
When I was hunting for an agent, I sent a one page query letter that described the concept of the book, who the market was for the book and my writing credits. No proposal.
However the proposal was completed before I even put the agent list together. If an agent requests the proposal you want to get it to them as quickly as possible. I did not include a sample chapter in the proposal but instead, gave them the first chapter of one of the previously published books to demonstrate the quality of the writing and the format. If this is your first book, a sample chapter is mandatory. You don't have to write the entire book for nonfiction. The sample chapter doesn't have to be chapter 1, choose the chapter that is easiest for you to write or the one you're the most passionate about.
My proposal included a description of the concept of the book, a list of people who had agreed to be interviewed, a list of competing books and why my book was better, why I was the best author to write this particular book, who the readers would be (the market) and how that market could be reached as well as, what I as the author would do to reach that market, and a brief bio including writing credits. Additionally there was a list of chapters with a paragraph description of each chapter.
After an agent agreed to represent the book, we (I have a co-author) then wrote a sample chapter, or actually in this case it was samples from two different chapters and was about 6000 words.
Hope this helps.
Dee