In case you didn’t know, Amazon has a plugin for WordPress users that are also members of Amazon’s affiliate program. The affiliate program allows you to monetize visitors to your site by promoting products and getting a commission if users click through to Amazon and make a purchase. I think the most successful thing is to promote products that you use regularly and can write a review about. Users are typically looking for reviews/recommendations and if you already have users coming to your site, promoting products that you find useful is a great way to add content to your site and monetize your visitors. I personally find writing a review about a product that I believe in to be better than putting another ad on my site.
The plugin from Amazon provides an easy way to embed affiliate links into your site. These affiliate links allow Amazon to credit visits/transactions to your account. If users don’t click on your links and go directly to Amazon, you won’t get credit. With the plugin, you can search for products and get real-time prices. There’s also different widgets and custom ad-units (but I don’t recommend these as they’re basically ads and users don’t like/click on ads).
The reviews for the plugin aren’t great with a current rating of 2.5 out of 5 stars. There’s a lot of complaints about the plugin not working and functionality only working if you’re already a member of the affiliate program with significant sales. So I would recommend only using the plugin if you’re already a member of the program.