As somebody in a similar age bracket, the things I do:
Stay healthy. My energy levels are generally great if I am getting plenty of exercise and good sleep. And avoid eating junk, throwing off my sleep schedule, or having big worries.
Do things that matter to me. A few years back I was doing consulting that I got burnt out on. So despite a very lucrative bill rate, I said, "fuck it" and joined a friend in a startup. He had a problem that I really wanted to see solved.
Work with people I like. If I'm going to spend most of my daylight around people, I want to enjoy it. I generally like people, so this one isn't too hard for me.
Serve people I like. If I'm making something for people I care about, this is a big motivator for me. It definitely helps for me to actually meet users, watch user tests, and see stats that demonstrate that what we ship is making a difference.
Minimize my commute. I know that some people don't mind long drives in traffic, but I'm not one of them. I live in SF and have occasionally done gigs down the peninsula; it quickly drains not just my enthusiasm, but my will to live. I want to spend my energy on things that are actually productive, and rush-hour traffic is not one of them.
I look forward to seeing what others say.