yes study sessions are excellent.. though.. the people you go with need to be motivated to study.. not go out and shop [ like i did!]
umm make a table of what your planning to study per session.. like how much time you are to dedicate to each topic..because then you would of at least covered everything that may occur with any exams or assessments, when you make up the table.. remember to leave extra time at the end so that you and your friends can go over any problem areas..
it's best if you do the topics in groups since, if one doesn't understand a particular part, but another does.. it makes life so much easier!
venues: usually library is a good place to start or someone's house away from any distractions and temptations!
timewise.: don't study straight for 3 hrs + your mind wonders, so take short interval breaks inbetween to stretch around, relax etc.