Can somebody help me with my bodybuilding routine?

I am a 17 year old boy and i used to exercise a year ago ( body building) not that intensive but just to stay firm. I am now going to start again and want some help with my planning. I am going to go to the gym 4 days a week and one of the days is going to be running and cycling etc. The other 3 days....... should i exercise two muscle groups a day? like shoulders and biceps, triceps and chest, abs and legs? Please help me chose the right pairs of muscle for a day Thank you!