I told this story last night, but it bears writing down. Some years ago, when I thought I was fighting against persistent low-level depression, a therapist advised me to try and notice my feelings. As a scientist I'm well aware of saliency biases and know that a good way to combat those is to take regular samples. My feeling that I was always unhappy might be untrue - a product of my remembering only or most strongly the negative emotions.
I developed a practice of checking on my own mood while walking from my apartment to the T in the morning and then back again in the evening. I tried to ask myself, honestly, questions like "Am I happy now?" and "Was I happy today?" Sometimes the answer was yes, sometimes it was no. I started to get a more realistic picture of how happy/unhappy I was. Doing this for several months instilled in me a habit I should practice more: noticing joy.
Last night I was having good conversation in a pleasant place, with good food and drink. My dinner company was delightful. I felt joyful and I managed to stop and notice it. To be more in the moment of joy, if I phrase it in the language of mindfulness I've recently learned.
This is an important thing for me to do in my life, and particularly as I head into SAD season. I'm told that this sort of thing comes naturally to other people, but it's never been that way for me. It's a practice and I'm working on it.