Don't overlook the rules. This is sometimes called the terms. Too often, people don't read the terms for the affiliate program and later become very disappointed. Know what you can and cannot do. Make sure you understand the rules, that you agree with them, and that you can abide by them.
Find out what level of support you will receive as an affiliate. Affiliate managers that offer their affiliates marketing information, newsletters, and an affiliates forum are generally great programs to join, because the level of support is high. It is obvious that these affiliate managers want their affiliates to succeed, and they are willing to help them find that success.
If an affiliate forum is provided, read through the posts and see what the other affiliates have to say about the program. This is a great way to find out if there are problems within the program, and to see issues what other affilates are facing in terms of selling the product.
With a little research and thought, you will find the affiliate programs that work best for you and your site. Don't rush in to anything. Take your time, and look at all of the information available to you about the program. If you are unable to find out much information without joining the program, go ahead and join anyway. Most affiliate programs are free to join, and if you find that it isn't what you wanted, or it doesn't meet your standards, simply remove yourself from the program.