The most sensitive parts of the penis are the glans, the coronal ridge (the rim of tissue separating the glans from the shaft) and the frenulum. One way to start a hand job is to stimule these areas, concentrating on the tip.
Some guys like it if you stimulate the penis with one hand and use the other one to caress the balls. Feel them in your hands, gently rolling them up the underside of the shaft, but never squeezing them.
When you stroke his penis with one hand, you can use the other to put pressure on his perineum. Press against it with your fist. You can also use the fingers of the other hand to stroke his anus.
Guys have different sexual preferences, so ask the guy his likes and dislikes.