You can lick the raphe from top to bottom and gently suck his ballsac into your mouth. This is another sensitive spot that deserves lots of attention. Keep one hand around his shaft with your thumb pressed against the frenulum, the sensitive tendon-like flesh on the underside of the head of his cock.
So how do you get started? Get on your knees when you’re stroking him, and you can easily dip your head to suck on his balls.