If your doing his whole body he needs to be undressed, If just his back then he only needs to have his shirt off. Unless you have a massage table the easiest way is to have him lay on the bed, then get on the bed on your knees, this will give you some height and make it easier to work those muscles. Kind of kneed with your fingers at first then you can start to use the palm of your hand a little harder. Using a nice smelling massage oil is also very nice. It makes it easier for you and the smell can be relaxing depending on what you use. I like to use Sandalwood aromatherapy massage oil. Make sure you have the lights off as well, perhaps light a candle for a relaxing mood.