I make myself happy by nurturing happy biochemistry.
When I notice myself becoming disharmonious I try to disengage from whatever I'm thinking at the end. If I still feel bad I go for a run or something and then, when I'm feeling more steady, try to solve the problem.
As for specifics that allow me best to trigger happy biochemistry...
I like being awake by myself at night, either on the Internet or just laying, almost asleep thinking, w/ my girl & my cats by my side, a couple candles going (about to go out).
Also, hanging w/ friends (have moved around alot & many of my good friends I've either lost touch w/ over the years or are gone). Walking for hours in the city streets or playing board games or sitting around talking about plans. Stuff like that.
Also talking walks by myself late at night (when the crazy world is asleep), thinking, jotting down ideas on lists (95% of it will likely not amount to much but I never know the 5% that WILL). Often my cats'll tag along with me and follow me (darting off the side from time to time but never lagging behind or running ahead more than a block or two) for miles until I get tired enough to sleep and head home. I like listening to music as I walk. One of my favorites perks of this high-tech world (that & the Internet), I don't take it for granted (maybe because I didn't grow up w/ it, didn't get my first stereo tape player until 14, my folks weren't really much for appreciating music, except classical, which I didn't care for much at the time but enjoy a bit of now).
When I didn't have a woman I liked daydreaming about having one & flirting online (although usually I'd prefer the phone since online you never know for sure who you're really talking to). Now that I do I'm forced to channel my energy into other things. It's hard because I'm insecure about my skillset, my ability to "succeed" in the world, many things, except wooing women (well, most of my life I wasn't really confident in that either but I got better since I've been an adult) which for awhile was my biggest challenge/excitement.
I only had one job I really got a rush (happiness) out of & that was being a bike messenger in New York. I loved that feeling of racing thru traffic, leaving cars in the dust, the feeling of eyes upon me (imagining women lusting after me & men envious when in fact people were probably mostly thinking I was a maniac
).
Of course there is also the intellectual excitement of learning new things (and then imagining future scenarios of using those skills or even better actually using them in some way, however small, right there in the present).
Hopefully the best in happiness is yet to come. I'm kind of tired of most of it coming mostly from what I'm dreaming instead of stemming from what I'm doing. It naturally becomes less and less; like a drug. Because truly we are hard wired to always seek true happiness. False happiness gets old, anything that does not genuinely satisfy the soul/brain does not satisfy for long. This is why I don't drink anymore & don't take drugs. I'd rather try to stay present and find some appreciation, even in the midst of extreme discomfort (not saying I always succeed but I'm always improving). Some people would rather get really mad/sad/etc. My GF gets like that sometimes. She plays the "I'm mad at you" game. We're all like little kids thinking the world cares if we're mad or sad or feel guilty or miserable. In fact, no one really cares so just make the most of it and move on.
Also, it's important you get out and get a life & don't waste too much time reading preachy platitudes from random schmos on teh Internets.