Last year, I had the privilege of listening to Bob Mayer speak at the Desert Dreams Conference on Independent Book Publishing. This field is growing fast so I admit I'm curious to learn more. I purchased the book he coauthored with Jen Talty, The Shelfless Book. I recently began reading my copy and have found it to be quite interesting. One piece of advice he gives to all experienced writers is to rely more on Beta readers (readers who don't write) to give feedback on your manuscript and not critique groups made up of writers. I am lucky I have people I trust to look over my manuscripts, both writers and nonwriters.
If you are interested in learning more from this NY Times Best-Selling Author, I suggest you pick up a copy of one or more of his books on writing.