Happiness for me is primarily about contentment and creativity. I do believe it's an inside job most, if not all the time. I think our moods can be and are affected by outward things such as money problems, loss, etc, but that true happiness can only come from within.
After many years of depression I learned on my own that getting to know and love (and forgive) oneself are the initial steps to happiness. From there I learned to be authentic...which can be pretty scary but, in the end definitely worth it. I think once you make that choice and have mastered authenticity and learned to base your life on your own values instead of other's values and opinions, happiness (or at least contentment) is inevitable. Getting to know oneself is key to finding what makes you happy.
For me and many others life would hold far less joy without a creative outlet. I think everyone has an innate need to be creative and I believe those who find their creative outlet in their work or can make it their work are far more likely to be happy.
I also believe spirituality can play a very important role. That too, I believe is an inside job. From my own experience, religion was of the things (if not the main thing) that contributed to my depression and feeling a lack of happiness. Trying to live up to everyone's standards (especially Gods) was a formula for failure and guilt. Leaving Biblical dictates behind and living according to my own spiritual and moral standards set me free far more than Jesus could or ever did.
That's not to say one cannot find wisdom in ancient texts and/or spiritual leaders. I agree with the Buddha, "Work out your own salvation. Do not depend on others. No one saves us but ourselves. No one can and no one may. We ourselves must walk the path."