One great way to get ideas for related products to promote is to look at the stats/reports that Amazon gives you to see which products readers are buying. After a while you’ll start to notice that they’re not only buying the products you directly promote but other products as well. Some will be completely irrelevant to your niche – but many times trends will emerge that could signal other products that it might be worth promoting.
You should also make sure you aren't competing with your own affiliates for eyeballs. Any marketing channels you're using, such as search engines, content sites or e-mail lists, should be off limits to your affiliates. Put marketing restrictions into your affiliate agreement and notify partners immediately. It's your program--you set the rules. Or, if you prefer, you can let your affiliates run the majority of your internet marketing.