My best advice to graduate students: enjoy!

If you're lucky, you have an advisor that teaches you much more than science and research. My advisor taught a lot about how to work in a political environment (yeah, universities are highly political environments).

If you are very lucky, you have an advisor that asks you to teach. By teaching undergraduate student, you learn all the small details of your scientific area. I was lecturing in physical chemistry as a graduate student - and even supervising undergraduates - and after a couple of years I knew all the fundamentals of physical chemistry by heart. That knowledge helped me through writing my thesis.