Find work. When you first start out, you may have to accept work writing about a topic you don’t find all that interesting. You must keep an open mind and be willing to accept work that may not be in your desired field. However, as you continue to write, you not only learn about more topics, but you also build your reputation. With time, you can be choosier about assignments you want to accept.
Now most affiliate programs have strict terms and conditions on how the lead is to be generated. There are also certain methods that are outright banned, such as installing adware or spyware that redirect all search queries for a product to an affiliate's page. Some affiliate marketing programs go as far as to lay out how a product or service is to be discussed in the content before an affiliate link can be validated.