I couldn’t resist the title on this one. It also seems to be a useful article in its own right.

Design Better with CRAP – lifehack.org

All design starts from four basic principles, abbreviated as CRAP (they come in no particular order, so the more squeamish can rearrange them to form “CARP”, if you like. I’d advise against “PCRA”, though…). These are Contrast, Repetition, Alignment, and Proximity.