It's essential to add one sentence from your research of the agent’s work: tell her why you want to work with her, specifically. Mention a book she represented that you liked.
Some writers wonder: Why not work into it gradually, maybe beginning with a sentence like “I love your agency and would love it if you represented my book”? If you’re the agent who gets two hundred query letters a day, imagine reading the “I love” sentence two hundred times a day. The letter would go straight into the round file. It’s essential to make that first sentence engaging, even electrifying—and about your book. You worked long and hard on that premise statement; now use it.
--from Catfish & Mandala by Andrew X. Pham (memoir)
--from The World of Normal Boys by K.M. Soehnlein (novel)
The Proposal Packet
Out of twenty agents queried, you may get a few who want to see your proposal packet. This packet contains a synopsis that gives the substance of your book, a chapter outline, platform (marketing niche) information if your book is nonfiction, and sample chapters, or the “partial.”
Fiction and Memoir Proposal Packets contain:
cover letter (your query letter can be reshaped)
bio (one page)
chapter outline (one to two pages, with two brief sentences about each chapter)
synopsis (one-page overview of the plot and meaning of your story)
sample chapters (usually two, or between fifty and one hundred pages)
Nonfiction Proposal Packets contain: All the above plus:
platform plan and marketing analysis (how you’ll help sell your book)