A general, but crucial point: When people type those keywords into the search engine, they are most often looking for information.
That's pretty obvious. But it took me a long while to realize it. When I started blogging I just wanted to express myself, so I started a couple of rant blogs about anything and everything. Opinion, comment and humor blogs do have an audience, and I built up decent traffic to them. But it's very difficult to sell anything off them because the readers who keep returning are usually looking for nothing more than an amusing or diverting point of view.
But if you offer good, useful information in the form of tips, guides and links to other good sources of information, and you keep it specific to a niche, then you can monetize your blog more effectively in the long term.
Firstly, you'll have a higher click rate on the contextual ads that you are showing, since they'll be more relevant. You'll also develop credibility as an expert in your niche, so you'll have greater success with the affiliate products you sell off your blog. People will think that the product must be worthwhile, since you are endorsing it. (That's why it's also important to find quality products to promote!)
So, a good question for money making bloggers to ask before every new post is: Is this informative and useful to people? I think that asking it consistently will help them build a leaner, more readable blog that is ultimately more profitable.