Mostly I say “fat fat fat fat fat fat fat” and stare at them. Sometimes I crouch down in front of their terrarium and sing until Liberace decides to join in with his awful awful singing voice.
It depends on the pet owner and the frog species. Delicate frogs like dart frogs you exclusively watch, they aren’t for touching. Larger species of tree frogs and many species of toads can be handled (mostly consisting of them sitting on one’s hand) once they get used to you. See the Stickyfrogs tumblr for an idea of this. Also, many larger frog and toad species are fed outside the enclosure- you take them out into a bucket or a little container and put their food in it for them. This reduces the risk of overly enthusiastic frogs swallowing substrate, and is a good deal of fun to watch.
You can also put Youtube videos where they can see. They’ll watch the motions.