I would recommend you each begin with one of the practice exams. Each of you take it at home under simulated (timed, no calculators etc) test conditions. When you get together to meet for the first time, go through each problem or as many of them as you can get through and discuss strategies for solving it. See how many different ones you can find and who can come up with the quickest route to the right answer. You'll quickly start seeing trends for using limits, units, simple physics reasoning tricks, etc. Often times the majority of problems can be solved this way. While you're doing this, you'll also learn where each of you needs the most work. If some of you need work in similar areas, get together and work practice problems from other sources, study that topic in HRW or Griffiths, and then a after some time of that, take another practice test and repeat.