Where to find out what your readers are really interested in
First, realize that more than likely you don't understand exactly what problems, concerns and interest your readers really have.
You know they probably have an interest in the broad theme of your website, but they also have detailed interests about price, problems, other alternatives, what actual users have to say and many other questions.
The second problem is that many times your readers are not as up to date or as educated on the topic as you are. After all, you live and breath the topic every day. You need to look at the topic of your site through the eyes of your readers.
One way to get the information you need is from Google Analytics.
You can also check your website logs to get some of this information. You can review the questions and comments you get from readers and check the time they spend on your different pages.
Also be sure to check the questions and comments on your competitor's blogs and discussion forms. See what's on their viewer's minds.
Bottom line: Don't just assume you know what information your readers want. Do your homework.