I've said it before, but I'll say it again. On one level, all these self-helpers, whatever their subjects may be--happiness, contentment, success, fulfillment--are talking about how to live. They all have these programs for changing yourself.
Maybe you're an outside-in kind of person, so you like Dale Carnegie's "smile and the world smiles with you" approach. Maybe you're more of an analytic navel-gazer, so you like assignments that have you come up with your values (Covey, for example). Maybe you're more spiritual, so you like Deepak Chopra's methods.
Whichever you prefer, I would like to point out that some changes are much easier to make than others.
Eons ago I attended a parenting talk at the younger daughter's nursery school. The school psychologist addressed the tendency people have to fall back into situations that are "comfortable" for them. Comfortable, in this sense, means "familiar," what you were accustomed to as a child. So if you came from a warm, open, loving, and supportive home, you'll tend to recreate that for yourself later in life. And if you came from a dysfunctional home where perhaps you were ignored or neglected or worse, you'll tend to feel "comfortable" re-creating these things in your adult life. Indeed, if you start feeling too happy, you might be uncomfortable, and screw things up for yourself until you feel "comfortable" again.