Top affiliates are fresh and original. Many affiliate programs provide their affiliates with pre-written emails, advertising copy, or articles. They also usually provide a number of banners that you can choose from. After you've seen the same tired old ad time and time again, it simply becomes ineffective. People will ignore it since it's been used too many times.
Top affiliates provide content.
If you are advertising a product on your website, try adding some solid content to your offer. Then tie the content into your offer, and show your visitors how the product will benefit them. Top affiliates don't use hype. If you use hype you'll end up with a dissatisfied customer who may return the product and spread the word about you. Keep your customers happy and they'll come back.