As a student: Say thank you and mean it to everyone you encounter that helps you in the least little way. Be appreciative of those who take the time out of their busy day to show you something, let you pass meds or perform a procedure even though it takes you a lot longer, or answers your questions. This profession can often be thankless and people deserve to know that they've made a difference to you. Even the gruff, standoffish, and mean nurses like to hear a thank you. Treat your techs with respect and ask, don't tell, them to do something. They are with the patients just as much if not more than nurses and perform a tough job for a fraction of the pay. They also are the ones who will be helping you clean up patients, find the linen cart, and navigate the supply room. Appreciate them for their role.
For when you graduate: The one piece of advice I will give to you is to NEVER forget what it is like to be a student and take the time to mentor them when you're a full-fledged nurse. Likewise, NEVER forget the first time a patient makes you feel like it's all worthwhile. It will keep you going even on the rough days.
What I wish I had known before nursing school: It all comes together at the end. As many others have described on here, one day I simply realized, "OMG I know stuff! I'm smart! I'm a nurse!" After all the care plans, exams, skills demonstrations, clinical mistakes, and countless hours studying, I realized that it all was a part in making me the nurse I am today. It will happen for you, too. Don't worry about how or when it will happen. I know this is fruitless to say because you will worry since there is so much material and so much stress in school. But keep in mind that one day it will and you will not always feel so lost and incompetent.