One of the most important aspects of affiliate marketing is testing landing pages. I have to admit I am not expert and have learned how to do test the hard way. With PPC costing so much I did not want to leave my landing pages to chance. There are a few books on the topic and I found that Landing Page Optimization: The Definitive Guide to Testing and Tuning for Conversions by Tim Ash is a great book to get started. It will put you in the zone. With landing pages it is important to make small changes and measure results. This is what Tim Ash recommends in his book. You need to always be testing and keep track of the changes made.