Gee thanks, Chris!
(I just noticed that I did the principles in the wrong order which makes the acronym CPAR - not quite as memorable.) For those who don't like C.R.A.P. your alternative is C.A.R.P.
(not a bad thing, since one you learn these principles you will be constantly carping about them.)
I think that all of us (well,
most of us) are equipped to make value judgments on aesthetics of a web site, magazine layout, ad layout, etc.
In other words, we know what we like (looks good) as opposed to what we don't like (looks unappealing). But what most of us
can't do (without a little training) is to explain WHY. What makes this look "good" as opposed to this looking "bad".
Generally, once you understand C.R.A.P. you
can explain WHY. You can look at a web site, or magazine layout, or print ad, and view it through those different lenses:
How are they using/not-using: Contrast, Repetition, Alignment, and Proximity? Once you can do that you can turn a critical eye on your own work.
It is not that there is only one way to do things. You could take 10 graphic/web designers and they will come up with 10 different designs/color schemes/etc. But if they are good, chances are it is because they all make use of those principles.