I have heard a lot about the categories that people do the best with on eHow, and most of it centers on legal and medical topics. I have heard many times that legal and medical topics pay better through Google AdSense and through eHow and similar sites because of the money to be made form the ads and the competition that exists for them. I have no medical articles on eHow and a very few that could be considered legal articles, so I can't say how accurate that is from personal experience.
But, there is something that has become very clear from looking at the amount that I have made for each article. The articles that are about hobbies, personal issues, etc., make small to moderate amounts. The articles that solve very specific problems are the ones that earn the most. My top earner has now made $120 and my second highest has made almost $70. These two and all of my articles that have made more than $30 are ones that solve a problem that brought people to the Web to search for the answer.
I have written several articles about astrology and how to deal with certain signs, etc. I've written eHow articles about how to make different types of crafts and about interpersonal relationships. All of these articles are ones that I think people just happen to look at rather than actually searching it out and scanning the page for all of the information they can get. Some of them have earned decent figures, but none of them have reached the amounts that the problem-solving articles have made.
To make articles about solving problems, think about topics that people will run to the computer to figure out how to solve. Instead of "How to Choose a Car," write "How to Negotiate With Car Salesmen." The first one is too vague- it's an article that people may run across, but they aren't running to the computer to find out the information. The second one is a specific-problem-solving topic. Instead of writing about how to keep mice out of the house, write about how to kill them. The first one may interest people when they are online and think about the topic or see a link to it. The second one is what will bring in readers who are craving the information, and those are the ones who will be interested in the ads on the page.