Affiliate sales comprise a large chunk of revenue for most big-name bloggers. For instance, Pat Flynn made $53K last month from affiliate sales, compared to "just" $9,500 from book sales. In general, look for affiliate products with higher price points; web hosting companies are a great choice if it makes sense in your niche, with payouts of anywhere from $60-$130+ per signup.
Affiliate marketing is a blog monetization method in which you place a link to a product or company on your website or a social media platform in an attempt to make an income from followers purchasing the product through your link (this is called an affiliate link). Affiliate marketing can be a great way to make money blogging because if there is a product or company that you enjoy, all you have to do is review the product and hopefully others will be interested in buying it as well.