I read this post by Alex Chu on the BW forum a while back and I found it very helpful, not just for b-school students, but also for applicants. It certainly helped me frame my thoughts on why I want to go to b-school and made me realize that b-school is not just about getting that coveted job in investment banking or consulting (both of which I'm not interested in anyway). Hopefully, it will be some use to you too.
Just make the most of the time you're there by focusing on things you can't do if you're working full-time. Cherish every day that you're not working. Consider it a privilege and blessing that you're basically taking a 2-year sabbatical. You didn't spend upwards of $150K and $150 - 300K in forgone salary to sit alone in your room and read books and do problem sets (if that were the case, you'd just get an online degree). Get fully involved in your b-school community. Learn from people - focus your efforts and time on group projects, stay awake in class discussions, go to as many guest speaker events/student conferences you can go to (you'll learn more from these speakers/alums/industry folk than you'll ever learn in the classroom), get involved in the fun clubs where you'll actually make real relationships (i.e. you'll make far stronger relationships playing basketball with your classmates than doing mock interviews for finance internships). In short, enjoy the journey and process of those 2 years - because the real value isn't the "goal" of finding a job or a post-MBA career, the real value is those actual 2 years itself where you'll grow both professionally and personally in ways that you won't when you are working full-time - simply because you are meeting all kinds of people you'd normally won't meet, having the time and opportunity to do things you'd normally won't do (skydiving, traveling with fellow classmates, playing more sports, getting involved in theater, etc.) and simply having 2 years of life where you're not working. In other words, you're not buying a "career" with your MBA, but you're buying 2 years of life away from an employer who would otherwise own you for those two years if you weren't in b-school. It's 2 years that you're buying to focus on YOU, and nothing else. In fact, it's not even 2 years - it's really only 16 months of actual school (8 months of class, then 4 months internship, then 8 months of class) so time goes by very quickly.
There's nothing real specific to do, since everyone is different, but it's all about having a healthy attitude towards the experience. Spending those 2 years on your own terms the way you want it.
The other thing is to be aware of the herd mentality. It happens at every b-school, and has happened since the dawn of time. Don't let classmates influence your career choices, what electives you should take, where you live, etc. MBAs as a group are by nature a neurotically insecure bunch -- as a group, they will cluster around and lionize what is "hot" more than what is right for them as individuals. If you can spot the hype, that's half the battle. If something sounds too good to be true, it is -- MBAs are easily suckered into believing anything so long as the prospect of money and exclusivity is high (i.e. making lots of money in an area that would be the envy of other MBAs). B-school is kind of like an ant colony actually, except there is no queen ant so all the worker ants are left to following each other. Be your own man (or woman).
Other than that, don't eat yellow snow, drink lots of water before you go to bed if you're drunk, and always know the name of the person you wake up next to.