It is important to get to know other members of the lab, including other students, technicians, and/or postdoctoral fellows. Learn as much as you can about the ongoing research projects in the lab, and possible projects for your dissertation research. The duration of laboratory rotation will vary from program to program. The research you actually perform during a rotation may be a side project, part of another person’s project, or an opportunity to generate preliminary data for a new line of investigation.
Other things to watch for include the style and culture as well as a size of the lab. Some students prefer to be in small labs, with more one-on-one contact with their mentor, whereas others may prefer a large lab with more lab members and perhaps more variety in research projects. You should find the right balance between your mentoring needs and the mentoring style of the faculty member.
Other issues to discuss with your potential mentor include: policies on work hours, sick leave and vacation; policies on authorship and attendance to professional meetings; and practices for publication in a timely manner prior to graduation. You should also talk with current and former students about their experiences in the particular lab.
In the end you will want to find a lab that provides an environment that is intellectually stimulating, collegial, promotes open discussions, and is emotionally supportive.