Publishers adore...adore...an Internet platform. It's one of the big changes that has happened since the Internet has entered so many American homes. Even before you send out that first manuscript, fiction and nonfiction authors should be developing a website, blogging, writing articles related to their themes for article submission sites, and sending out press releases related to those same topics. It's a low-cost way to build groundswell without having to leave home.
Once that portion is underway, everyone should develop keynote addresses or brief talks related to their themes. The articles and press releases are the starting point...anything important enough to discuss in those items can become a topic.
Common mistakes for both fiction and nonfiction authors:
The biggest one is probably thinking that a single shot of anything is going to generate results. I've talked to many people determined to sink their entire marketing campaign into a single full-page ad in the New York Times. They expect that sales will roll in and provide financing for any additional marketing the might opt for later.
This is wrong. The basic tenant of all sales is that the product or author's name must appear 7 times before it's recognized; it takes another 5 to 7 appearances before people are actually motivated to buy. That's in part why the multi-pronged approach works so well...it shoots out the same information in different formats to different outlets and creates the multiple impressions required to drive sales.
Another mistake: thinking that a website is the advertisement. Actually, a website is a destination...it's like you have to sell the site in order to sell the book.
A website doesn't do any good if there isn't any traffic coming in, so treat the site like a product. It's free but you want people to engage with it so they will engage with your book.