The content is everything you do to pursue your readers to buy the particular product following your affiliate link.
You need to create highly valuable contents that should be far better than the sites currently ranking in the top 10 for the keywords you are targeting.
The content you produce for your niche website must be 100% original. No spun or rehashed content will work for your niche site on this post-panda era.
Many niche site projects fail because of some simple keyword research mistakes.
Step by step keyword research guide for amazon niche site. For niche site builders, Keyword Research Is 80%, and rest of the process is 20% of the job.