Some ideas for things to try in your study group:
1. Compare notes on that week's lectures. The sooner you do this after the lecture, the better. Don't recopy -- just fix up the parts that weren't clear. Fill in any details you missed and be sure you understand the major points of each lecture. If there is an example, ask yourselves, "What is the point?" If there is a principle, ask yourselves "Do we know a good example?"
2. Go over the study questions, old exam questions and/or recitation questions. Force yourselves to explain the answers to each other without using pronouns. Don't use "it." Say "microtubule" or "microfilament" or "tubulin." That way you are sure you all know what "it" is.
3. Give each other sample questions or quizzes -- take turns making up a question or two for the others to practice on.
4. Make summary charts and diagrams and/or other study aids. ("Make/Share/Compare")
5. Make a vocabulary list of all new terms for the week and check that you know the meaning and significance of all of them. (Don't waste time writing out definitions of all the terms -- spend your time on the terms that are unclear.)
Can't manage to form a study group? Still prefer to study by yourself? In that case, try all the ideas above but try to explain to yourself as clearly & thoroughly as if you were explaining to a fellow student.