Here are some great resources:

1)   The Copywriter’s Handbook by Robert W. Bly. A step-by-step guide to
writing copy that sells.

2)   Independent magazine. Helping publishers achieve and succeed. published
by IBPA (Independent Book Publishers Association. Published six times a year.

3)   Authors Guild. The Authors Guild supports working authors, advocates for authors’
rights, and provides a community for our members. The Authors Guild is America’s
oldest and largest professional organization for writers and provides advocacy
on issues of free expression and copyright protection. Authors Guild website