Look through your Achievement list. You don't have to do everything, but just looking through it and seeing what kind of content the game has achievements for should give you a starting point for finding content to do. There is literally enough content in this game to keep you busy for the rest of your life, it's just a matter of whether you want to do it or not, either because you find the content enjoyable or because you want the rewards. Just ask yourself, "What kind of content do I enjoy?" and "What kind of rewards do I consider worth working for?"