This is not a book on how to be happier. It is quite the opposite. Daniel Gilbert explained how people are not happy like they thought they would be.
Happiness is a product of actions which require calculated prediction. How can we predict? We imagine. We imagine if we choose plan A over plan B, how would our lives be. Then we choose to act according to our expected utility associated with consequences of both plans.
Imagination, however, contains three shortcomings. First is realism error. We fail to imagine every feature and consequence of a future event. We choose to act from too little our brain can be aware of. The second shortcomings is presentism. The imagination of the future is based on today's materials. But well.... What makes us happy today might not make us happy tomorrow. We are rolling stones with a tendency of thinking we are trees. The third shortcoming is rationalization. Imagination is a drama bitch. Bad things are not as bad. It is why people who experienced pains/tragic life events can much happier than who didn't. Resilience cures sadness.
All in all, what should we do to be happ(ier)? 1. Prefeeling is important. You feel right then you do it right. Stop imagining and expecting too much.
2. Seeking advice from everyone. Most people think we are unique. No, uniqueness is a mainstream diva (not real and never speak truly). Scrape off all the thinking that you are different, you are unique. Solutions are all around us and many tackle your difficulties. Copy them and you will do just fine