1. Find a program you currently use and would recommend to a friend. This makes your recommendation honest, and personal.
2. Go to the company's website and see how easy it is to purchase a product from their website. After all, you won't be earning any commissions if people can't buy from their website.
3. At Shareasale.com they have a list of the top 100 affiliate programs. This is a great tools to show companies that (one would assume) have made it easy to purchase products on their website. When you are looking for an affiliate program you might want to look at this list to see if any of the products you would recommend to friends. Do NOT pick a program just because it is having high commissions. It has to FIT you audience.
There are more tips in my book More Podcast Money.