You need a central theme to talk about on the blog. There are a lot of blogs that are all over the place without having a central theme or idea. There has to be a central theme on the blog so your readers can understand what you are trying to communicate. It doesn't have to necessarily be about the Affiliate product or the industry, but you will need to have a subject that is identifiable. 

You don't need to be a professional writer like Stephen King. All you have to do is just have something that you are knowledgeable about and carry the reader through each step of what you know. As long as it relates to the Affiliate product you are promoting, then you can add value to the program. 

Everyone knows that a good looking site can keep a visitor's attention for a while but you have to make sure the blog visitor knows what he or she is looking at and has to flow. It doesn't matter how beautiful your site looks, if they can't get the information they are looking for, they will just simply press that back button. You have to make your layout very user friendly and not complicated or fancy.