Speak up: If you have ideas that the group hasn't thought of yet, or an interesting solution to a problem, speak up! Don't let the opportunity slide because you are afraid of the suggestion would sound. Chances are, your suggestion may be a good contribution, or at least get the group thinking in a new direction.
Listen: If your group member has some concerns about the direction the group is heading, listen--and listen to everything that they say, don't just wait for them to stop talking!
Step up and step back: Basically a remix of the earlier points. If you are constantly dominating the conversation, pause and ask what your group members are thinking (step back). Actively encourage everyone's participation. Likewise, if you are shy and quiet, challenge yourself to speak up when there is room in the conversation (step up).
Keep each other updated! If you are working on one aspect of the project, but you get sick and *gasp* the progress report is due, your group members should still be able to turn in the progress report without you there. You should be talking to each other constantly.
Lead when you are supposed to lead. If you have been tasked with one area of the project, and you drop the ball, you are not only hurting yourself. You are hurting your team members, and you are not being a good leader.
Respect the division of labor. Check in with each other, and make sure the sharing of work is equal. If it is not equal, then it is still no excuse for your entire group to drop the ball. If there is a major deadline coming up, make sure you are communicating with your group members, and that the job gets done at the end of the day.
Take responsibility for your actions. If it was your job to do a task, and it did not succeed, own your part in that failure. Don't look around for excuses or someone else to blame (your teachers can see right through that).
Conflict is normal! We are all different, and we're going to have different ideas about what is the best way to proceed.
Have a plan. Whether it is voting, asking outside opinions, or just rock, paper, scissors, it is good to have a plan on how to handle conflict. Just as long as you don't avoid it completely.
Be respectful. At the end of the day, these are your classmates, and you will be sharing space with them for the next three years. Work it out, and let your teachers know if you are hitting a serious roadblock that you can't get around.