You first must choose your keywords. This is perhaps the most important step of the process as incorrectly targeting phrases can result in traffic that is not interested in your product. There are three tools that I use virtually every day to help pick the most appropriate keywords:
The last in the list is the most important. Look through the potential keyword phrases and think, "Who would be searching using that phrase?" If the answer is, "a student looking for information" then chances are it won’t result in a sale. If the answer is "Someone who is looking specifically for a product I offer," then obviously this is a prime candidate as a targeted keyword phrase.