Using keywords in order to pull traffic to your affiliate program is one of the easiest ways to make that program profitable. People do it in several different ways. They pay for the traffic through pay per click, they build webpages surrounding those particular keywords or they use article marketing in order to rank well. Any one of these methods can work but if you're not targeting the proper keywords, your sales will be slow.
Finding the right keywords takes a little bit of practice but once you get the hang of it you'll be surprised at how easy it is. There are plenty of places where you can search for these keywords online. Wordtracker and the Google keyword tool being two of them. Instead of focusing on one or two word phrases, search for longer phrases as they tend to have less competition. These are generally referred to as long tail keyword phrases.
You're also going to need to get into the mind of your visitors. Once you have exhausted all of your options, try to think of other things that people may be searching for that would be interested in your product. Use synonyms, plurals and anything that may be associated as these could also pull in the right kind of traffic. Make sure that you track your traffic to see where the sales are coming from.
So, if you want to find your success with affiliate marketing, you need to use the right keywords. Spend a little bit of time every day in this particular form of marketing and it won't be long before the sales start rolling in.