Study these
Hand-job Techniques Too many girls don't know anything about hand jobs, all they do is go up and down. Pick about six or seven of the ones listed in that link and give him all of them. Listen close to his moans to figure out which one he likes the best. Be sure to try the "Twist and Shout", that looks like the best one to me.
And don't get him to cum too soon with hand jobs, When he cums, he won't be able to feel the sexual stimulation afterwards, so cumming basically ends your hand job session. Practice some tantric hand job sex, right before he cums, stop for a few minutes, then switch to a different hand job technique.
Just for an example, you can try these in order:
Endless Stroke
Twist and Shout
Glans Head Massage
Milking
Spot Pinch
Shaft