Either after I've pasted my content in, or even before, I like to find images that best suit the subject matter. These will either have to be photos you've taken yourself, or are public domain. Or it might come with conditions, for example, you might have to credit the photographers name and/or provide a link to their site or profile page.
Some people rely on a Google Image Search, but those images aren't free. There are plenty of good free stock photography sites out there, just be sure to follow their rules as to attribution.
Next, think about whether or not there are Amazon products that will complement your topic. If I were writing about dogs there are plenty of products you could choose from. Dog toys, accessories (leads, collars, etc), grooming products, even books. Even more specific than that, if you published an article on say Pugs you'll find that there are books (dozens in fact) about that particular breed.
Always keep the product placement in context with the content. Go to the effort to pick and choose the products you think best fit with the theme of your article.