Umm, well, it does depend on the fellah, I think. I do know that with a circumcised man, the bit just around the base of the glans, where the foreskin was removed, can be really really sensitive... I have found that finger and thumb forming a ring, well lubricated, just circling that, move them back and forth (that is, round and round), with your lips and tongue just sucking and flicking over the glans... can be extremely good. Works pretty well with non-circumcised men, too. Some men find it too much, bit like getting it too hard/directly on the clit for some women.

Not all the time, obviously - alternate with other things. Forming a vacuum to make a real sucking feeling can be good. I use my hand to guide & add extra stimulation all the time, or gently rubbing balls, unless of course I happen not to have any hands free at the time...