Amazon operates a volume-based advertising fee structure. The more products that are shipped as a result of your affiliate links, the more you'll make per sale. Once you have sold enough products to move up to a different advertising rate, all subsequent sales will give you commission at that rate, until and unless you reach the next fee level. Note that some products are exempt from this commission structure.
Affiliate Marketplaces – ShareASale and ClickBank have thousands of merchants to choose from. It’s nice to login to 1 place and check the performance of multiple affiliates without going to each individual portal on each website. Many programs aren’t part of a marketplace though. I’m a big fan of ShareASale – there are so many companies and industries you can choose from.
If you’re writing reviews, you should 100% be using rich snippets (they add review stars to your search engine snippets and increase click-through rates). There are many WordPress plugins for this but my favorite is WP Rich Snippets. It’s $69/year (or $399 one-time) and I use it for every single review I write. They have tons of add-ons, settings, styling options, and looks nice. Free plugins like All In One Schema.org do work but lack settings, styling, and flexibility.
Register in least 10 forums and try to post at least 100 comments in every forum. However, don’t spam in the forum otherwise you account can get ban. If the forum is relevant to your product, you will surely earn commission in your first few days. Test the product if it is performing good, then post more comments, otherwise change the product and start promoting that one.
Whether you have a website or are still dreaming up ideas for a blog, you can also look into affiliate marketing. With affiliate marketing, you partner with brands and businesses within the content of your website. If you mention a product or service, you link to that produce or service using a unique affiliate code you received when you signed up for that particular affiliate program. From there, you’ll make money any time someone buys a product or service through your link.