Keyword research is one of the first things you need to focus on if you want long-term results - before traffic or content strategies. If you're not targeting the right keywords all the traffic in the world (paid or otherwise) isn't going to help you succeed. Let's look at how keyword research will set the foundation for a successful website.
The number of monthly searches and competing pages in Google aren't the only things you need to be worried about when researching keywords. Even if you find a keyword that has a lot of searches and almost no competition, it's not going to be very valuable if the searchers aren't able to take action when they hit your site.
In other words, you want to look for targeted traffic. That means people who are willing to spend money or who are looking for information that you can provide them in return for some type of monetization.
A lot of internet marketers fail at this point. They choose keywords that might get a reasonable amount of traffic, but aren't very effective at generating revenue.
You can find buying keywords in several ways, one of the most effective being common sense. Some words are obviously not very good for finding buyers, such as anything with the word "free" in the phrase. If people are searching for "free dog training guide" do you really think they're likely to buy the one you're selling on your site?
Specific keywords, such as product names and model numbers, are generally a lot more likely to convert visitors to buyers. eg. If someone arrives at your site after searching for "Sony TV model 123 review" they're a lot more likely to be ready to buy.
Google is another effective research tool for identifying buying keywords. If you search for a keyword with Google and there are zero or very few paid ads, chances are it's not a very good keyword to target. "Undiscovered" markets are few and far between so if there are no ads running chances are other marketers have already tried that keyword and failed.
These non-buying keywords can still be useful if you're building a site for natural search traffic. Just target the ones that are going to result in more profit first, and then start expanding.