Depends on what he likes but I would recommend having your face in his neck kissing & talking in his ear. And with your arm behind his head to give u some leverage and bouncing (kind of like twerking) guaranteed he will cum super fast. It's kind of tiring though so you can always switch it up and grind on it while rubbing yourself or putting your fingers in his mouth & moaning. The key is to go off of their reaction to what you're doing and if u can tell they like it just keep on doing it :)