The California Science Center's website is a great way to review with the students what they will be learning or seeing while on their field trip. It allows you to click on each exhibit, and gives a general description of what each room contains.http://www.californiasciencecenter.org
I would also make sure that I was planning this field trip around a unit which focuses on what our class will be seeing. This will require careful unit planning. This is important for the students to better grasp the concepts while receiving hands on demonstrations of is being learned in class.