Games for Social Networks

You must not include calls to action in the body of your Stream stories (e.g., “Beat her score!” or “Can you beat her score?”). A call to action must only be presented as an action link (in line with “comment” and “like” and similar to Facebook’s stories in design).

The above quote highlights one of the bigger changes that the new set of pages at the Facebook Developer Wiki explains with examples. Developers need to design, or re-design, their application's virality and retention based on these constraints if they are to succeed both in the eyes of their players, and Facebook policy management.