Many authors stop at writing a book or two, but an often overlooked and powerful marketing tool is articles. These articles, if well-written, organized and submitted in a timely fashion, can lead to all types of other free publicity for you and your book(s). This works especially well for nonfiction authors, but can work for any author. The trick is finding a way to write in the area of your book's target audience, though there has been more than one cross-over success.
When you begin seeking out venues for your articles, don't overlook the places such as Helium or social network notes and bulletins. Your own blog and the blog of friends are great options, as well as ezine publishers and webmasters. Look at what other successful authors are doing. It may seem tedious in the beginning but the rewards are endless.