If every study group member has a laptop computer, you can each create an outline as you move through the material. One strategy you want to avoid is the one used in the movie, The Paper Chase where each study group member outlined a different course, then traded outlines. In the movie, it was a disaster. In real life, it's extremely risky to rely on someone else. If you take the approach of just helping each other with each course, you'll move through the material more quickly and be more likely to catch each other's errors.
Study groups can also be disasters when there is competition among the study group members.
You have to remember that you are there to help one another. Even the brightest person will get some things incorrect that the others will pick up on. Another danger in study groups is to get unfocused and start gossiping about fellow students, professors, politics, etc. This can turn into a great time-waster. When your purpose is to study, keep the peripheral stuff out of your session.