Read the literature. Ask the PI questions occasionally about a new paper in Nature, Science, Cell, etc. Don t spend too much time doing outside activities in the lab. Everyone surfs the net a bit or checks their e-mail just make sure that you aren t doing those things every time the PI sees you. BUT this is often not the case.
Appearances are important.
First impressions are important. Yes, these are petty. But doing at least some of them may keep your PI happy with you. Rotations are not necessarily representative of what it is like to be a graduate student in the lab. During your rotation make sure you ask current graduate students and others around the lab lots of questions to determine if the side of the PI and lab that you are seeing is the same as their daily reality.