The narrower your topic, the more focused your web site, the better your chances of being ranked highly in the different search engines.
This doesn't mean, of course, that you won't have your ebook listed in topic-wide ebook directories. It simply means that you also need a finely-targeted web site that talks about your ebook's pinpoint subject.
For example, you can have your career-related ebook listed in the general or multiple-topic ebook directories and even in sites that feature jobs and careers. But your own web site should deal mainly with a particular small area such as: "interviewing tips for thirtysomething women."
Sure, focus. But focus on what? Afterall, one can write a pretty specific book about the dating patterns of sodium electrons on New Year's Eve in the 1900s but will that sell?
TIP: Here are the broad topics you can start from when trying to get down to your chosen specific subject:
And here are the related phrases to add to your ebook's title:
Let's see this in action -- Imagine that your ebook is about orchids:
Most of the ebooks on the web talk about making money online or how to make money selling information products or how to attract any member of the opposite sex.
Isn't it time to write about your particular hobby? Something to think about.
Remember, focus your topic and hook it to one of those three major ones: money, health and relationships.
According to a New York Times article ("Struggles Over Ebooks Abound" by David Kirkpatrick, November 27, 2000), few people read entire books on-screen. I personally find it such a strain to read off of a monitor.
Some usability experts suggest that online text be 25% of the length of printed text.
Then again, Philip Greenspun's Travels With Samantha has scads and scads of text yet still remains popular. (Although I really wonder how many people read his stuff word for word online.)
So here's a TIP: Cut-out 75% of what you would have otherwise printed. You can later offer the 100% version as a printed book if you clearly see demand for it. You can also offer the 100% version in electronic form for those who prefer to print it out themselves.