It’s something akin to picking stocks. You want to buy undervalued domains, and sell them later on at a higher price. For example, you can pick a domain that is out of favor, but could be related to some future event. So if you decide that the stock market is likely to crash in the future, you can buy a domain that includes the words stock market crash during a rising market, and then sell it in a falling market.
Research individual companies in your desired niche: If possible, it’s always better to become an affiliate directly with a company (if they have an internal affiliate program), as no one else will be dipping into your commission rate. This is the preferred route for most of the prominent affiliate marketers, including Pat Flynn. Unfortunately, it’s also the most work, as you’ll have to do the research yourself to see who offers programs (they’re usually listed in the website footer).