Yes and no.
In some ways, you should prepare for an open book exam the exact same way as you would prepare for a closed book exam. You should make good outlines and know them cold. You should commit your outlines to memory. You should never feel as though you depend on your outline being in front of you to answer a question – even if you have the option to consult it throughout the entire exam. The best students barely consult their outlines at all during an open book exam.
However, there are two things you should do differently for an open-book exam.
First, tab your outline! You want to make sure that your outline (and anything else you may want to refer to during the exam) is tabbed and organized so that you are able to find whatever information you are looking for quickly and efficiently. The last thing you want to do is waste valuable time flipping through your outline or notes.
Some students find it helpful to make cheat sheets (or even use our law school one sheets!) for law school final exams. The idea is to have all of the rules at your disposal so you can easily find and copy the rules. It is also a great idea to try to memorize the rules ahead of time, as noted above (and if your goal is to do excellent in law school, it is imperative that you understand and memorize the rules the best you can!). But having a excellent, organized outline is a great idea for an open-book exam!
Second, practice your analysis! In many ways an open book exam is actually more difficult than a closed book exam. Professors are not as impressed with rule statements (since you have them all right in front of you!) and they expect a very good analysis and application of law to the facts. This means you should take a lot of practice exams prior to the actual exam.
So another tip for open-book exams is to practice exams and make sure that you focus on writing a stellar analysis.