how hard are handjobs?

How picky is your man about technique for giving him a hand job? I just want to see if I'm doing something wrong. Note: he doesn't masturbate either so it's not an issue of me competing with his own abilities. My husband and I try to do this (and we don't do oral-his choice and I agree), and I feel like I suck at it? But at the same time I feel like I don't. He'll keep giving critique and such during it and it makes me hyper aware and then I try too hard and I get worse. But I feel like he is very preferenced as to which places on the penis, the angle, the pressure, etc. and has to have it exactly perfect but it's different every time, in order to come, and I can't get him there. We'll go for more than 20 minutes until my arms are sore and my body is sore in various places from leaning towards him. How big of a difference does lube make, because we don't use it; as long as we don't get sweaty, the skin doesn't get sticky and it isn't unpleasant for him. But does lube take everything I'm already doing to a different level?