I haven't been out of school for very long - although, of course, it seems much longer. But for those that are about to graduate, I have a few pieces of advice for you.
1. Travel by yourself, in a place where they don't speak your native language, for a long time (a few weeks at least). This is the most important thing I ever did for myself and I recommend it to all my friends who go through a rut, all my interns, all the people that seem like they're a bit lost. It will do wonders for you because you will do things you cannot imagine doing in places you can't imagine being. You will learn your limits then, so you can push them later. Just do it, don't think about it. I recommend picking somewhere lovely and warm.
2. Make a goal for every year. I usually just make one big one - a whole list of resolutions are useless. One distinct point in the future helps me focus, is realistic, and at the end of the year I can say yes, I succeeded or no, I failed. Not yes to some, no to some.
3. Keep track for a week of every hour of your day. Literally write out a list of 24 hours with what you did each hour. Add them up into categories and see how you spend your time. This is how you find the time to learn a new language, go to the gym, cook meals instead of buying fast food, etc. etc. For all those times you ask people how they have time to do all the other random things they do, now you'll know. We're all given the same amount of time each week. Some of us just use it better -- make sure you're one of them.
That's it. There's a lot of the abstract advice that other sites and people will give you -- but these are three very grounded, real things you can do for yourself.
And don't forget to go on vacation before you start a job.