Wiley, a large book publisher of literally thousands of book titles has a free PDF with some good marketing advice for the aspiring author. Although meant for standard novels and the like, much of the advice will work well on RPG releases and board games. I especially liked the focus on creating a blog about your product, review importance and the “how to make a promotional video” sections. “An Author’s Guide to Online Marketing and Publicity” is a free download and only 34 pages, so it is a quick read.
Trask, The Last Tyromancer