The best way to develop a strong fan base for your non-fiction books is to become well-known in your niche. Given a choice, readers will always buy a non-fiction book written by someone they know and respect, or have at least heard about. But how do you go from being a complete unknown to becoming the go-to person for your book topic? Controversy! 
For every topic popular enough to warrant books, there is some sort of controversy with two opposing view. In quilting, it's washing fabric vs. sewing straight from the store. For puppy fans, it's crating vs. letting a pet have the run of the house. Even if the controversy has absolutely no bearing on your personal life, it's extremely important to the people who will buy your books. Latch onto one side or another and you'll have at least half the readers in your niche looking to you for answers.
Starting Your Campaign
Your base of operations will be a website with a blog. Use one of the free sites, but spend the small amount of money to get a memorable domain. Make it something that stirs the emotions of the readers you want to entice. Write short blog posts once or twice a week, covering different details of the controversy. Use logic and humor to make your side seem like the place to be, but show how much you know about the topic. Feature your book front and center as proof that you know a lot about the subject.
Spreading the Word
Look for forums and websites with chats that are dedicated to your topic. Join in the conversation as much as possible. Be pleasant and polite, but state your case as strongly as possible. Don't forget to pass out your website address as much as possible. The object isn't to gain followers to your cause, it's to show people how much you know about the subject and to get them intrigued and wanting to know more.
Increasing the Conversation
Host weekly Twitter chats on your controversial topic. Issue invites on the same forums as you appeared earlier. Do the same thing with Facebook chat events, and even Google Hangouts talks. Mention your book to increase your credibility as well as to increase sales to anyone who hasn't seen it before.
Start a Newsletter
Continue the conversation by starting a newsletter about your topic. You only need to produce a new issue once a month or so, just enough to keep your name connected with your topic in readers' minds. Include breaking news, opinion pieces, and information about your next book on the subject. Once you've got people interested in you as a topic expert, they're a natural audience for buying the next book you publish.
Keep the Faith and May the Force be with You!
