Bibliotechula on Chronicle forum had this to say:
One thing you might want to do is contact editors before you even send your proposal and ask about their publishing plans and plans for their lists in the coming 1-2 years. That will give you an idea of who is acquiring and who isn’t, particularly in your area.
Send your whole ms to a few trusted colleagues and ask them to write blurbs for you. These are not full reviews, just brief, positive comments on what your book will add to the field. You’ll want to include these in your proposal packets when you send everything out again. You might also want to send your proposal packet to an advisor, mentor, or friend to give it a once-over. I’m not necessarily talking about typos, but fresh eyes might help you craft a better-selling proposal.
You may need to tweak your proposal to make the topic seem “hotter.” A little spin can at least help you get the sample chapters reviewed.
Be sure your proposal packet includes a market analysis and some kind of information about your target market. If an editor sees a potentially large target market, the more likely s/he will be to send the ms out for reviews or at least look at it more closely. Even UPs are driven by income, if not profit, and many now are for-profit. If there is an extra-academic market, like high school or a particular group of people, make sure to mention that.
It seemed to me to be sound advice and thoughtful. So I wanted to save it and put it somewhere it was easily accessible, for me, rather than on the 47th page of the fora lists.