Always warm up before you workout, reason why is because you want to prevent any injuries from happening. Remember you can’t completely prevent an injury but you can do things to lower the chances of having them. Also you want to warm up to get your energy levels up.

In my opinion a good warm up would be 3-5 minutes on treadmill, beginning with a walk and then last 1-2 minutes a run. After that going into the primary muscles being worked and stretching those muscles out. Next would be finding your first workout, for example squats and doing reps with no weight, around 15-20 reps, then going into your first set of 50% of your 1 max rep 5-10 reps and now you’re fully warmed up and ready to begin lifting heavy weights.