1) Listen to everyone's ideas - Instead of going on with the first suggested idea, let everyone speak of their own idea and let the whole team decide which idea to finally choose by elimination.
2) Participate actively - Instead of sitting and doing nothing, make the most effort to come up with ideas and help your group members. Encouraging a group member who is not interested is not a bad idea either
3) Be open - Be ready to accept it when your own suggestion is not finalised. No matter how much you think that it would work, do not argue with your group members and cause disputes between the group. Try discussing the pro and cons about your idea and the finalised idea.