Listening.
I've found that as I listen to the little voice inside of me, no matter how difficult it may be, I am happy.
The little voice might tell me to not eat any more of the donuts or Almond Joy's that are in my desk, or to stop checking and re-checking my e-mail and Facebook and instead get a little more work done, or to put the dishes away, or to make dinner, or to read a book, or to study the scriptures, or to write in my journal, or to go to bed... All of these things are things the little voice tells me I should do instead of sitting around and being lazy. Basically I find that I'm happy when I stop putting off the more important things I keep meaning to do. I guess they have a name for this sort of thing - prioritizing. (And not being lazy!) And not only that, but putting less important things behind more important things. A talk comes to mind, Elder Dallin H. Oaks' "Good, Better, Best" from the October 2007 General Conference. President Dieter F. Uchtdorf's "Of Things That Matter Most" from October 2010 General Conference is also a goodie on this matter. This is something we could all benefit from I'm sure! I know I have. I'm trying to be better at listening. And even though it's hard sometimes, I find greater happiness in doing instead of doing nothing.
Gotta love the amazing gift of the Holy Ghost. I would be so lost without Him.