My main advice is to 1) intermingle licking/sucking his shaft and sucking on his head, 2) suck and stroke his cock at varying his rates, 3) suck on his balls (at varying points you are doing the above), 4) lick from the head of his cock to his hole in a masterful swoop so it seems effortless and seamless, 5) stroke his cock while you tongue fuck him - if he lets you - 6) finger his ass while you paying attention to his cock - again if he lets you - and 7) kiss him and stroke him when it seems right. At all times, I use as much saliva as possible. And I try to mix things up as much as possible. The highest compliment I have gotten is after the guy came as the result of a blow job he said to me, "It was like you were making love to my cock."
P.S. Incorporate nip play if it seems that gets him hard.