You must feel comfortable talking and asking questions of your professor. While related to the above, this is clearly a separate consideration. Be sure your professor isn't too hands off or too hands on for your liking. Professors can be thought of as kings and queens of their labs and some act like it. Some people are unaffected by being the focus of fits of rage, others are quite bothered.
Labs usually reflect the professors tastes and vary greatly with cleanliness and order.
While there is the aesthetic component to this question, many labs handle radioactive materials and other biohazards that make mess, clutter and dirt risky. Find a lab where conditions allow you to work comfortably. After a full rotation through a lab, a professor's personality will be readily apparent. However, students get only three rotations out of the hundreds of possible labs. Thus, it is important to make decisions based on the above before choosing their rotations.