StephenR and bcowan hit the nail on the head. It's all about finding your passion and then focusing on a handful of affiliate programs that fit your niche.
When I first started on the web in 1998, I bought a lot of affiliate marketing books too and I became an affiliate for them. I was basically inspired by Allan Gardyne of AssociatePrograms.com, but after a while I realized I didn't have the following that he has so it was difficult for me to compete in a saturated niche where there are so many gurus.
I thought I could just add a bunch of sales pages on my existing site to get people to buy them. My site wasn't really content-rich, it was just a bunch of sales articles trying to push these products.
So I shifted my focus and built two websites on topics I enjoy: web design and fitness. I created a bunch of content on both sites and sprinkled in Adsense, along with affiliate programs that relate to the theme. My income started pouring in after about a year of building.
You can do it! Just pick topic FIRST, then find programs later. Don't become what I call a "backward affiliate" Those are the ones that join the programs first and then build sites around the products. Choose a topic you're interested in and then go from there.
Good luck!
