Lick It Like It's a Lollipop
This one is often used in porn films, because it allows him to see exactly what's going on. It's best done on your knees, and depending on your heights he might need to stand on something (you need direct access to his testicles). Start by lifting his penis to expose his testicles, then find the line that runs up between them (it's a tiny ridge that's often a darker color). Find where this starts on the underside of his testicles, and that's where the long lick starts '- continuing, very slowly, right to the tip of his penis.