I am starting to go to the gym. This may be a silly question- but, what do I do while I'm there and for how long?? In the past, I have usually walked on treadmill or used bicycle for 30 min for cardio and either called it a day and left or did some of those weight/resistance machines for like 15 min. I don't know what you are supposed to do but I want to max out my trips there so any advice would be appreciated. Thanks!