The answers to this question are as various as individuals are - that's what makes our species so interesting! But the bottom line is that the more love we put into an occasion, a relationship, a "work," the happier we are. Even the happiness that comes from owning a new possession comes, in part, from the happy occasions we envision in which we'll "share" this possession with others - a bike run, a family trip in the new car, lugging a passle of kids to camp. The deeper our capacity for God Who is Love, the deeper our capacity for happiness.
Proverbs chapter 3 in the Book of Proverbs ("Mishle," to our Jewish friends)and in early Christian circles called "Wisdom," gives an even deeper perspective into what makes us happy:
"Happy is the man/woman who finds wisdom, the man who gains understanding..." And what is wisdom? " Trust in the Lord with all your heart, on your own intelligence rely not; in all your ways be mindful of Him, and He will make straight your paths. Be not wise in your own eyes, and turn away from evil. She (Wisdom) is a Tree of Life to those who grasp her, and he/she is happy who holds her fast."
If we are truly wise and trust in the Lord, Proverbs tells us, we serve the Lord with confidence, and serve our neighbor with kindness. Wisdom teaches us to let go of our envy of the rich and famous, to let go of senseless quarreling, to let go of dishonest talk.
If we "get our heads straight" with Wisdom we allow the Lord to lead us unerringly, and life, whether awake or asleep, whether we are troubled or questioning, has a sweetness and peace that at times can seem unfathomable. We are lifted up into the gently swaying branches of God's Tree of Life, and its roots reach into the depths of the Universe.