Depends on your goals, experience, and knowledge of use.
IMO most people have no need for it. If just looking to get big then gear will do that.
Anyway, 4 weeks on 4 off max. Personally I would take longer breaks but depends on why you are using it.
I would start at 2iu pwo with a protien/carb drink followed by a meal 30 minutes to an hour later and have glucose tabs on hand at all times. Then build up by 1 iu a day until you reach your desired amount. Typically guys shoot for 10 iu pwo but 6-7 would be plenty. Some guys like it pre workout but you run the risk of going hypo while training and I don't like that idea.
I wouldn't go over 10 iu. I would also always have glucose tabs or something similar with me even after it's supposed active window. Most people prefer humalog because it's fast acting. I hear hard gainers like humilin r because it a little longer acting. Either way, know the active length of which one you choose and be prepared to deal with symptoms.