Robin Williams describes the fundamental principles of design, for a non-designer, in The Non-Designer's Design Book. A funny mnemonic for remembering these principles, which the author is hesitant to spell out in the book, is C.R.A.P, short for Contrast, Repetition, Alignment, and Proximity.
We want to avoid elements that appear similar, and almost a cardinal sin when the elements are clearly unrelated. Contrast is how we communicate, and nudge the observer towards the intended elements of focus. Contrast can be achieved via type, color, size, shape, and even whitespaces.
A good design should be clearly identifiable through repeated visual elements, whether it be color, type, layout, and so on. Repetition is what gives design the unity of belonging to the same objective. Repetition is also what eventually gives design its brand.
Well-aligned items are pleasing to the eye. A concious alignment also conveys a sense of vigor and seriousness, that an otherwise arbitrary placement of elements would not.
All the design elements should be grouped by relation. This avoids confusing designs where the eyes need to jump all over the canvas to comprehend the contents. Good design, avoids clutter, maintains low cognitive overhead.
In addition to its fluid exposition on design principles for the lay, I found an another extremely appealing principle, which is rather generally applicable.
Once you can name something, you're conscious of it. You have power over it. You're in control. You own it.
This somehow resonates so well with scientific writing! Finally, a concluding quip from the author:
Listen to your eyes.
One of the first things I did after reading this book was to flush the contents table on this page to the left. This was earlier floating to the right, and had an ugly whitespace squeezed between the text and the table of contents box. The principle of alignment in action!
I share the design taste of the author, and as a consequence the book appealed to me right away. I still found enough byte-sized knowledge to absorb. Highly recommended!