Does it have to be sexual in nature? There are many things that you could learn to do that could entertain your Master that don't neccesarily have anything to do with sex. For instance, learn to do a good lap dance, or belly dancing (check out some Shakira videos on youtube) that's hot, or maybe there is something else that your Master finds particularly enjoyable to watch, or a certain kind of food that he likes and you could learn how to cook it. Service to our Master's does not always have to be sexual. If that's not what he always requires then there are unlimited opportunities to learn something that would please him.