In addition to the points as mentioned in the previous posts, new affiliates also need to learn who to advertise for and what programs to cooperate with.
Players want unique information and services in order for them to come back to a certain site.
Unfortunately there are still tons of affiliates supporting the worst operators imaginable. Not only does this get themselves in trouble as soon as the first payments do not get honored by foul companies, but players will run away too. Any affiliate needs to understand that he/ she also has a big responsibility towards their visitors.
After all there is much more behind it than many people would ever expect.