I don't really have a trouble getting all three stars lol. (though being familar with management games helps a lot) Really, multitasking the name of the game here. (aka let customers fuck you while doing shores) and don't forget to use your stamina to speed up the tasks (especially because as you have sex, you will gain some stamina reserves and there is a hard limit on how much you can save up) so the "secret" really just pressing R to use stamina until empty, collect the stamina reserve when it's full, rinse and repeat.