Information that helps readers take an action is always more valuable than information that helps your readers think. In marketing terms, that means that your target market is people who are looking to buy / acquire something and are looking for ways to do so. It's what we call the 'end of the buying cycle' your best chance at getting your prospect to buy something is he makes a purchase.

When you are looking at topics, you can use the metrics mentioned below as a means to judge whether a topic is worth pursuing or not, but when you are doing keyword research, make sure that you target those keywords that prospects will be searching for when they are collecting information that will help them make a positive / negative buying decision. An easy way to determine the profitability of a topic is to measure it by the 'PPC metrics' which are Popularity, Price, and Competition.

Popularity

In crude terms, the more popular the topic is the more clicks you will get on your ads and the more chances you will have of converting those prospects into customers. Higher popularity means more profit for you. On the other hand, popular topics are already very competitive (in most cases), so you have to analyze it from all sides. Low-popularity topics can also turn good profits, so just because a topic does not get 100,000 searches a month does not mean you shouldn't go near it. The key is to match all these factors popularity, price and competition before making a decision to target that market.

Price:

The price of the product you are promoting will determine your profit margins. With high priced products you can afford to spend more money per click, and that's mainly why you see such outrageous bids for terms like real estate, insurance, lawyers and pharmaceuticals they can afford it because making a couple of sales gives them huge profit margins.

On the other hand, with products with a low price point you will have trouble going overboard with your bidding, and you will need to be very careful with what you're willing to pay. In such a case, keyword research becomes even more important as you absolutely must find those keywords that you can target cheaply.

Competition:

What is your competition like? Heavy bidding will suggest one of two things either the market is lucrative enough to risk investing so much money (back to the 'price point' discussion above) or there is someone trying to price their competition out of the market. In either case, you wouldn't want to spend too much money at the start, so this step will give you an idea of whether you can enter a niche without getting totally burned. Another point to consider is that if there is low competition for a topic, you have to figure out why that is. Is it because the niche isn't well known?