One of the best pieces of advice I can offer a new grad student is to find time each week for a non-school related activity -- sports, hobby, etc. This should be something fun and, preferably, something you do without any of your lab buddies. This probably sounds easy, and perhaps obvious, but when the work starts to pile up, it can be very easy to neglect your own self.
I've been dancing since I was six years old, and dance has always been a big part of my life. When I first started at my current university, I was reluctant to seek out dance opportunities because I already had so much on my plate -- trying to navigate a new school, learning to balance two residences (my first house, with my husband, and my apartment at school), and planning a long-distance wedding. About 6 weeks after moving, however, I had a huge argument with my fiance (we've fought maybe 3-4 times in the 9 years we've known each other), and the very next week I came down with the first migraine I'd ever had. We both agreed that it was time for me to to start dancing again.
When I'm at dance, everything else disappears, and I get an hour or so to focus entirely on me. It helps me work out the frustrations of the day; it gives me a chance to express myself in a wholly different way than I do at school; it gives me an opportunity to interact with people with differing interests from my own... This week was my first week back to dance after a one month "summer break." I didn't realize how much I missed it. Already, I'm sleeping better, waking up more rested, dealing better with all the things that are going wrong in the lab right now. It's a wonderful thing.