I have found that one size doesn’t fit all. Rather, specific types promotions of particular products work well with Amazon. I have also had some success by getting people in the Amazon door for other reasons. For example I’ve experimented a couple of times on dPS with running a posts that gave readers a hypothetical $1000 to spend on photography gear and asked them to surf around Amazon and choose what they wanted to buy. The result was 350 comments (a fun community building exercise) and quite a few sales and commissions!
There are many ways to get people onto your list. Lead magnets are one such resource. For example, you can build ebooks, checklists and cheat sheets. But you can also do content upgrades, such as PDF versions of an article with added resources in them, four-part video training series, and more. Think about your audience and what you can offer them to better serve them, then treat them with some respect and you'll eventually reap the rewards.
The one thing to be aware of with WordPress Amazon affiliate plugins is that you don’t want to use one that offers link cloaking. This is a method used to protect affiliates from a threat known as affiliate link hijacking. However, Amazon expressly forbids the cloaking of their links, so you’ll want to avoid plugins that do that or always be sure to disable that functionality if they give you the option.
Selling graphic T-shirts is big business. Customized T-shirts with clever sayings or graphics are ideal for online sales. Sites like Teespring allow you to sell customer shirts. Teespring’s unique model allows you to design the shirt and get buyers lined up to purchase it. This saves you from the initial investment in stock and the time on processing and shipping orders, though you’ll likely make a smaller profit on each shirt sold.
Take good pictures. Some of the options below don’t require you to actually take the picture and sell the product, but for the ones that do, make sure you take a clear picture that makes your product stand out from the others. If you’re going to be taking a lot of pictures, set up a small “studio-like” area in your home with a backdrop and proper lighting to really make your pictures come across as professional. And of course, you’ll want a good camera too.
Set reasonable expectations for earnings. You've only invested $20. You're going to make 5 percent on most products. That means that you need to sell $400 worth of stuff to make back your investment. You get credit for purchases customers make while at Amazon besides just the product you linked to, so it's not as hard as it may sound. It won't make you rich, but it's not hard to be profitable, and the income builds over time.