I reduced my caffeine use from the equivalent of about 100 mg per day to one cup of weak green tea in the morning (10 to 20mg?) after reading that "deep sleep quality seems to stay effected for days after even single doses of caffeine.". I had previously assumed that most of the effects of caffeine wore of after about 8 hours with me, and that if it didn't affect how quickly I fell asleep, it probably wasn't affecting my sleep. I now suspect that it was causing me to wake up too early in the morning (although I think this started in the past few years, so something else combined with caffeine was probably responsible).
At roughly the same time as I reduced my caffeine use, I started trying meditation after reading good things about it at LessWrong. I'm disappointed at how hard it seems to be to learn (it seems to take increasing willpower to avoid having my mind cluttered with the usual mundane thoughts, much like after losing weight it takes a lot of willpower to avoid gaining it back), and I'm not noticing the benefits described on LessWrong (I've found that books on positive psychology have had more effect, although those effects developed slowly enough that I should be patient with meditation). But I suspect it's improving my mood in some subtle way. I need to experiment more.