All affiliate marketers should have a solid grasp on this topic, especially anyone running traffic on search engines.
There are a few points you should keep in mind when creating a keyword list. Pay attention to the depth as well as the breadth of your keyword list. A deep keyword list basically has a root keyword with many variations of that keyword (including misspellings, etc). A broad keyword list has related and lateral keywords, and this is the key to finding less saturated keywords that will cost less per click. When you first launch a campaign, its more important to go broad – this is how you will find sub niches. Once you find a few keywords that convert, go deep on those keywords.
Let’s say an affiliate is running a female diet campaign. If he developed a deep keyword list, he would have one keyword with many variations, for example:
Lose weight, lose weight fast, lose weight now, how to lose weight, easiest way to lose weight, tricks to lose weight, etc…
If he developed a broad keyword list it would look more like this:
Lose weight, alli diet pills, diet tips, low fat recipes, cellulite reduction, biggest loser, acai berry diet, fat flush, stomach staples, etc.
I just came up with these words off the top of my head, but I hope you get the idea.
An affiliate running a diet campaign might do his broad keyword research by reading women’s magazines like Cosmo or watching shows like Oprah. Or, talk to some girls and find out what products they know about 😉