Combined with the advice from BigDH01 and DaveSimmons, I would say that a marketing class would be handy. As a previous professor once told us, "If an advertisement doesn't capture you're attention, then it wasn't meant for you." That said, your GUI should be geared towards the audience. If you're making an app for senior citizens to balance their budget (I know, rough example), you don't want it to have flashing icons and complicated interfaces.