The time spent playing intramural sports, working on the school newspaper or just hanging with friends is important. Research indictes one of the most important causal factors associated with happiness and well-being is the meaningful connections with other human beings. One benchmark of your postgraduation success should be how many of these people are still your close friends in 10 or 20 years.
Marry someone smarter than you are. You will do better in life if you have a second economic oar in the water.
Don't model your life after a circus animal. Performing animals do tricks because their trainers throw them peanuts or small fish for doing so. You should aspire to do better. You will be a friend, a parent, a coach, an employee—and so on. But only in your job will you be explicitly evaluated and rewarded for your performance. Don't let your life decisions be distorted by the fact that your boss is the only one tossing you peanuts. If you leave a work task undone in order to meet a friend for dinner, then you are "shirking" your work. But it's also true that if you cancel dinner to finish your work, then you are shirking your friendship. That's just not how we usually think of it.
Don't try to be great. Being great involves luck and other circumstances beyond your control. The less you think about being great, the more likely it is to happen. And if it doesn't, there is absolutely nothing wrong with being solid.