Heidi shares a post from David Cain on his blog "Raptitude":
 

Gratitude, when we do genuinely feel it, arises from experiences we are currently having, not from evaluating our lives in our heads. When you feel lonely, for example, simply remembering that you have friends is a dull, nominal comfort compared to how wonderful it feels when one of those friends calls you out of the blue. Reflecting on the good fortune of having a fixed address is nice, but stepping inside your front door after a cold and rainy walk home is sublime. 

The experience, not the idea, is what matters. So if you want to feel grateful, forget the thinking exercises. Look for your good fortune not in some abstract assessment of your life situation, but in your experience right in this moment. What can you see, feel, hear, or sense, right here in the present, that’s helpful, pleasant, or beautiful?

There’s always something, any time you look. Any interesting sensory experience or pleasant feeling will do: the warmth of a space heater, the cat on your lap, the play of sunlight on the table.

That’s the other important part: we don’t need to reserve our gratitude for the big, lifetime-scale conditions, such as health, economics, or loved ones. In every moment, regardless of your problems, your experience is being improved and beautified by all sorts of small, often haphazard pleasures: the color of the sky, the embrace of this sweater, the protective shelter of this building, the peacefulness of this neighborhood, the taste of this coffee, the softness of this chair, the chirping of these birds, the alertness of your mind right now.

Of course, all the abstract, big-picture life conditions have their own corresponding present-moment pleasures, and they are what matter. Consider the world of difference between trying to appreciate the notion that you have a home, and appreciating the real-time experience of getting into bed in your own bedroom. That’s where your good fortune truly resides—in your experiences, not your thoughts.

Cultivating gratitude this way creates a completely different relationship to the good in your life than simply revisiting in your mind the logical reasons you ought to feel grateful. You’ll appreciate so much more of every day, even bad days, when you look for the small pleasures of present moment experience instead.