I'm not super knowledgeable about this, but I do know three people who are reasonably successful non-fiction writers (2 traditionally published and the 3rd entirely on the kindle store).
One thing they've all told me is that one of every publisher's first questions is something along the lines of, "How big is your email list?" The pretty much want writers to have already built up their own audience online.
One thing they've all told me is that one of every publisher's first questions is something along the lines of, "How big is your email list?" The pretty much want writers to have already built up their own audience online.