There are many ways that fiction and non-fiction authors can market in similar ways...for example, book tours, book trailers, having a great media kit, having a website, and so on. However, in some ways I think that non-fiction authors have an advantage because they can market to sites that focus on their topic as well as traditional book sites.
Additionally, I think it's easier for non-fiction authors to do radio interviews because they can give 10 Tips on how to... whatever the topic of their book is. Or they can do 7 Ways to...again, on the topic of their book. With fiction authors they mainly have to talk about the plot and their writing and that is not as easy as a non-fiction topic, in my opinion.
I think it is easier to market non-fiction, especially if you are self-published. I think it is easier to find and hit your target audience.
Unless you have a new twist on all the old themes and are extremely clever with words, most of the fiction out there is same-o, same-o. So if I find a good author I stick with them; Janet Evanovich and Barry Eisler being two of them from different genres.
I suspect I'm not alone as someone for whom the following sentence (from an article I just wrote for the IBPA Independent) applies: "It was fiction and narrative nonfiction that inspired me to shift careers into publishing after working among other things as a bookseller, publishing executive, and journalist, but I have no illusions about the likelihood that it will continue to be business and informational writing that pay the bills."
Personally I find that marketing nonfiction is much more straightforward and, except in rare circumstances, more powerful. Attracting nonfiction readers online begins with focusing on a clear sense of who my readers are, why they need what I am publishing, and how I can connect with them in ways that are persuasive without being intrusive. Keywords, search optimization, blogging, and networking can come relatively easily on the Googlezon web, and they are likely to produce readership if they are seamlessly connected to quality content and a highly searchable title and subtitle.
Fiction is a bit more of a lottery -- it depends to a large extent on quality within the terms of a given genre, on connections and hand-selling, on having a story as an author (and a human) in addition to the story you are telling, and on appearances that penetrate the real worlds in which readers live. Most fiction, even a lot of prize-winning fiction, exists way out on the long tail. George Plympton once made a telling remark about how the dependent the circulation of the Paris Review was on its own contributors and would-be contributors, libraries, and MFA matriculants -- from which I take the point that it is always important to cultivate other novelists as readers of novels, other poets as readers of poetry, etc.
Meanwhile, just to try and loop back and close my own polemical circle, I am always charmed by the savvy implicit in fiction titles like Nick Hornby's How to Be Good.
I am a non-fiction writer with my topic on integrity. My current book is titled Integrity: Do You Have It? 2nd edition. I feel that marketing for fiction has similarities with non-fiction as mentioned in another answer but there are unique differences for non-fiction. Non-fiction is based on facts for particular subjects while fiction may be based on some facts but the approach dictates it is fictional. There are events that have taken place in history where authors have taken the initiative to put a story behind the events. Some have even been developed into pictures.
Non-fiction authors do not fit this option in most cases. The non-fiction book depending on the subject has many advantages by searching for sites which relate to the topic. It helps to target an audience that is interested in the subject. My topic of integrity is something that affects everyone and people of all age groups have expressed interest in the topic. This being an election year integrity is an important issue when we decide upon a President and members of Congress.
Another important option with non-fiction allows articles to be written around the topic and with that I have written over 100 articles related to the topic of integrity. Issues in the news offer ideas where focus can be placed around the topic of integrity. Many times issues covered in the news offer new opportunities to gain exposure and recognition for your insight and expertise. My articles have done this. As a non-fiction author I feel there are more opportunities for interviews and other media exposure with a non-fiction topic. There are sites which focus on specific issues and some offer the opportunity for interviews.
Your topic or expertise for a non-fiction book also offers more opportunity to expand connection with sites which have wide appeal for the topic. The more their site is recognized in the search engines and the more visitors they have offer greater exposure for your work. Through my marketing activities I have seen increased exposure for my topic from sites I never knew existed. This is something that is an advantage over fiction books and the marketing opportunities available to non-fiction authors.
If you are looking for marketing information and opportunities you can visit my site www.myqualitywriting.com. It is a resource for other authors by providing marketing information/opportunities and I have received many complements on the amount of information that I have collected. If your book is family friendly I offer opportunities to increase your exposure. I have established through author interviews with questions directly written for each author. You can visit my site to see the type of questions I have asked others. Another option I offer is an online book catalog and if you are available for speaking engagements I have an online speakers bureau. If you are interested you can email me with the type of information that is posted for other authors on my speakers bureau.
It depends on what type of non fiction you are talking about - there are so many different genres and they are all different ! The approach needs to be different for each of them, as the market is different !
I'm another non-fiction author and there are many different types of non-fiction. There are advantages over fiction books because you can target radio shows, websites, forums etc. but the fact is you're going to have to do the work. Nobody knows your topic (and book) better than you!
Start with the basics that we share with our fiction brothers and sisters like website, blogs, etc. and then build on the foundation with targeted non-fiction marketing.
The basic approach to marketing fiction and non-fiction books would be the same.
There are marketing avenues open only to fiction writers and also marketing avenues open only to non-fiction writers. Then again, depending on your topic and target audience, you would have even more ways of marketing your product.
So in short, it's a case to case basis. There is a basic marketing formula that would work for all books, but also a unique marketing formula depending on your book topic and target audience