"The more time that individuals spend with their partners, best friends, and close friends, the happier they are. When they spend time with people who they dislike or when they spend time alone, their happiness levels drop. Loneliness is a relatively good predictor of unhappiness." (Mogilner, The Pursuit of Happiness: Time, Money, and Social Connection)
1) Spend time with the right people.
2) Spend time on the right activities.
3) Enjoy experiences before the experience (without spending time actually doing them).
4) Be aware that happiness changes over time.
"Don't let the noise of others' opinions drown out your own inner voice. And most important, have the courage to follow your heart and intuition. They somehow already know what you truly want to become. Everything else is secondary."