From a UMich site:
"One way to understand moods is that they are just the habit patterns of our mind continually playing themselves out in different scenarios. According to the view of dharma, we don't need to understand them or consider them so much as we need to replace them with new habits. This is where practice comes in. When we practice, we involve our body, emotions and mind in a new habit which is much more "real" in the sense that it is in line with the reality of enlightenment. This is the definition of purification. The problem with paying much attention at all to emotional states is that we must on some level believe that they are real if we are considering them at all. We reinforce our sense of egoic reality by examing and exploring them, much in the way Narcissis was enamored of his reflection. When we come to practice from that place, we create extra obstacles and encounter even greater resistance." -- A'dzom Rinpoche
Too wordy.
Be happy!
Not wordy enough to be quite true.
It depends upon what you mean by paying attention. If you pay attention to your emotional states in context (as opposed to surrendering to them), that is if you simply observe their passage through your body, and are alert to their contradictions, you can learn a great deal, and lose a tendency or two.
After all, meditation is little more than the slow objective observance of one's emotional states - to observe how foolish they often are, and that they are not you, you must in some sense observe them.
Westerners in particular need no encouragement to be unaware of their body or the subtlety of their emotional states - that much we already know how to do.
As for the shorter advice above, I'm afraid that for most of us, without a spiritual practice the advice "Be Happy" is no more useful than the advice: "Be a goldfish." Half of Buddha's point is that we don't know what happiness is, and mistake mere relief or distraction from pain for true happiness.