When we go to a physical shop to get something, we expect to pay money for the goods we obtain. But when we go to a website, we bring with us a different mindset. We expect information, goods and services free of charge. Because of this, advertisements about things that your visitors can obtain free will usually fare better than those about things that they have to pay money for. If your affiliate program has free stuff on offer, try them out on your site to see how it performs.
Traffic is Everything No visitors, no money.
To have people clicking on your banners and taking up the offers given there, you need to work on the traffic going through your site. There's no substitude for this. No amount of fine-tuning of your advertisements is going to help you if you have only a few visitors going to your site each day. Remember that not every visitor is going to click on your banner. So to earn some income at all, you really must generate enough traffic.