This one simple information-theoretic principle is an effective guide for user interface design: Things that are the same should look the same, and things

This one simple information-theoretic principle is an effective guide for user interface design: Things that are the same should look the same, and things that are different should look different. Your UI conveys information to the user, and the user has finite cognitive capacity for receiving and interpreting that information. So keep the the signal-to-noise ratio high! In my experience, a large portion of the user experience problems in real products are consequences of violating this principle. Construed broadly, this principle implies many design guidelines, e.g.: - If the user changes something, make the change immediately visible - If internal state affects what the user can do, make it visible - Don't use nonstandard interface widgets or icons If you can get this right, you're a lot of the way there.