This is a follow up to Sci's advice for undergrads. I know some schools don't do rotations but mine does. So here are a few pearls of wisdom for you noobs.
1. Study for classes. If you fail out you are worthless to the labs, plus you undergo extra scrutiny when you have a less than stellar academic record. Your committee will catch a whiff of the intellectual lightweight stank and pounce on you like a fucking lion on a zebra. You don't need great grades, just good ones. Also don't burn up too much time studying that you could be spending in the lab. I've watch many a rotation student study themselves out of a lab because they spent all the working hours of the week studying and not in the lab. You've got plenty of time at night and on the weekends to study.
2. Be on time. Remember that the senior graduate students and postdocs who you may be shadowing and working with don't view you as a future trusted colleague. The hard fact is that you are likely ill-prepared and not educated enough to immediate contribute to what they are doing and you were heaped on them by a PI. So be on time and do what they say to do when they say it and if they give you homework, you damn well better do it. Sure somebody trained them, but they are training you, be appreciative of it too.
3. "We used to do it this way" This is for those of you with a little bit of experience. No one cares how you did it wherever you came from. This is how we do it here. STFU, you haven't earned the right to an opinion! You will soon, but don't go telling us how you did it and how we should too.
4. Technicians are like gold. Treat them as such, they will bend over backward to help you if you show them respect. And lets face it most of them have been doing science longer than you and at a higher level than you ever have. Remember we are the transients that come and go, they are there to stay. Also remember that technicians, especially the lab manager, tends to be the eyes and ears of the lab for the PI. While you are in the lab, you have a well oiled covert spy system watching you, act accordingly.
5. The PI's time is worth more than gold. Don't bother them with trivial shit. They are also not really there to be your friend, drinking buddy, or shoulder to cry on for personal problems. PI's are happy to see you when you are generating data or need some help on the project, so if you want face time you've got to come with the data.
6. It's all a game! Learn to play the game and you will get to the finish line faster. This means doing things that placate your PI, learning who to go to for what you need, who to go to in order to get out of doing stuff. Also a big part of graduate school is learning how to say no to certain things that are of no benefit to you and your project and prioritizing what you are going to do.
7. Have fun. Its hard and its a lot of work, but its also a lot of fun. In all of my random jobs I have never worked with a more diverse and interesting group of people.