The solution depends on what you care more about.
If you care about your grades, study hard and spend all your time studying. If you care about social activities, you can join various clubs and make friends. If you want to work in the student union, you must behave well and try to undertake some specific affairs of the student union that you are good at. So according to what you care about most, choose one and work hard. If you want to take the postgraduate entrance examination, maybe the first one suits you best.