Jane Friedman has a background in publishing, including several years as Editor of Writer's Digest, so when she writes about the publishing industry, she's certainly got the background. She also has a Twitter following many would envy, and a successful blog.
Publishing 101 is a compilation of posts from her blog, and is well worth reading, particularly for what she calls beginning or early career writers. She makes clear that there is no "secret" to becoming a best-selling author, and the journey is going to be different for everyone. This was especially illustrated when she was talking about how she gained 100,000+ Twitter followers--she recognises she got a lot of those followers because she was the editor of Writer's Digest, which isn't a path open to everyone!
The focus is on those who are aiming for a traditional publishing contract, although a large part of the book is actually talking about marketing. In this she reinforces the advice I've read from other authors on the importance of having your own self-hosted website/blog and mailing list, not relying on external sites like Facebook (particularly relevant given the changes coming to Facebook in early 2015 which will affect the ability of authors to promote).
Overall, recommended for people seeking reliable information about publishing.