I've been successful at affiliate marketing for many years -- thousands of dollars a month -- with Commission Junction, Linkshare, Google Adsense, and Clickbank. I've made some money with Amazon but their terms and payouts are not favorable and don't use them anymore. And not so much with Clickbank anymore -- too many garbage products.
So how was I so successful when other people are not?
Before I started with affiliate marketing, I created a web site on a niche topic related to car leasing, a topic that many people were looking for information about. I chose this topic because it was something I already knew something about. I worked long and hard to create good content, and to build up a large number of visitors.
Then, and only then after having a lot of visitor traffic, did I begin finding affiliate programs that offered products or services that would be of interest to my visitors -- car insurance, car warranties, car loans, car accessories, car products, etc.
It worked. I began getting huge checks every month. It's slowed down some now that there is more competition for my web site. If you have a new web site and there are many other similar sites, you won't get the traffic you need to be successful at affiliate marketing. It's certainly not easy. It's hard work just like any other successful business but it's great to know that your work pays off and that you're making money while you sleep.
In summary, you can't throw up any old web site or send out unsolicited emails and have any hope of being successful. You must have a web site on a specific niche topic that gets at least a few thousand visitors a day, AND find affiliate programs that offer products or services that are directly related to that niche. You can't expect to be successful with an affiliate program that sells weight-loss products on a web site about cars. It's not a match and won't work. And you MUST have good traffic -- no visitors, no affiliate sales.
I hope this has helped.