There is a small secret as well to earn additional income that I have found to be most helpful, which ever affiliate program you join and put up on your site make sure that you do the following for the following reasons:
Have great SEO work done on your site, this will help boost you’re ranking in the natural searches and most recent studies show that 60% of traffic comes from natural search (see, www.webpronews.com) for reference.
Add Google AdSense to your site, this will help you get crawled that much faster (that part of course is arguable, but it worked for me, after adding it to my site I had double my pages indexed in less then a week). And because if the product you are offering does not appeal to you visitor one of the words in your AdSense program might, and you get paid when they click on it so it wasn’t a total waste of a visitor, plus you gave them another reference to help them find what they need, which is always a plus. You may even want to add a search bar to your site from another affiliate that pays you when searches are done through your site. There are many ways to make a program work for you, make sure you do all your research and have designed your site for maximum performance for your end users and of course for your revenue.