Search engine optimization is a process by which you write your web pages to make them more "search engine" friendly.
The only problem with this scenario is that by making your pages more "search engine" friendly you make them less people friendly, which makes them less "search engine friendly."
Now if you think that's all a lot of mumbo jumbo, it's not. What search engines are trying to do today is find web pages that are more people friendly. In other words, they are looking for pages that are relevant to the terms people are searching for.
So the secret to search engine optimization is to write for your visitors and not just for search engines.
After all, your visitors are the one's you need to please so they will feel comfortable making a purchase, or in the case of an affiliate take your recommendation and click on a link.
SE's don't care how your site looks, they just want to know if your page is relevant to the terms people have plugged into their little search boxes.
People are going to earn you money, not SE's. Write for your visitors!