I assume you've already picked the right keywords and an aged expired domain so...
1. Write long content, 2000+ words.
Content must be:
Well formatted
Engaging or keeps the reader interested (Questions, topics, unique scenarios)
Super informative (Research all the questions regarding the product and then answer them in your articles) Google pays a lot of attention to questions and answers.
Media rich. You must have photos, comparison tables, and a 1 minute video makes a big difference as well.
Your call to action must be strong! Remember, the whole point is to have them click that amazon affiliate link so you can drop your cookie. Amazon will do the rest.
Example:
http://bestreviews.com/best-jump-starters (Copy these guys and you will kill it with amazon)
2. Silo structure your website or at least categorize it very neatly.
Have a very fast and clean wordpress theme.
3. Pick the right server. Website speed plays a huge role in bounce rate and bounce rate plays a huge role in SEO, and seo in traffic, and traffic in profit. It's all damn connected lol
4. Get an SSL certificate. Improves ranking.
5. Make sure you have super mobile optimized website (50% of traffic is mobile).
6. Push notifications (google it, learn it, install it, use it)
7. Set up Google alerts for your product keywords. When someone asks about it somewhere else you go answer and drop your product review link. This way you will drive traffic and build backlinks.
8. Turn your product reviews into youtube videos. Create a channel for each website. Send the traffic from your videos to your review site by making the videos shorter than the actual review on your site and telling the viewers if they want to learn the key factors before buying they should checkout your site.
9. Get some paid social media updates by users with large organic following. These have great positive impact on SEO.
10. Open a reddit thread with a question about your product. Then go and answer it with a different account and drop your website link.
11. Paid ads rank you faster. This i learned from personal experience. Google will favor whoever spends money on Adwords, and whoever says this is not true is a fool. We came to this conclusion with a couple other big online business owners at a damn Google conference lol
12. Please do your research. There is literally SECRET SAUCE type knowledge about amazon niche sites shared FREE on this forum by some amazing contributing members that i need to go and personally shake their hands. I should buy them a beer as well. If you don't learn how to do proper research and dig deeper obsessively you will fail. Also, network with other amazon niche marketeers, everyone went through a learning curve and discovered tricks of their own. Becoming a true friend will allow you access to that type of knowledge.