CRAP stands for Contrast, Repetition, Alignment, and Proximity. These stand for the four principles of design.
Contrast is good…it attracts the eye. Contrast is the difference between medium blue and dark blue, for instance. Go bold or go home.
Is there a theme or brand running through your site? If so; take that color, logo, shape, line thickness, etc and repeat it throughout to organize and unify. Be careful not to overdue to the point of becoming boring.
Nothing should be put on your page randomly. Pick a side….alignment, that is. You really should try not to use more than two alignment styles. Envision an invisible line running down the page. Alignment doesn’t just apply to text either.
Like or similar items should be group close-by to each other to create one visual unit. It reduces a cluttered look, and organizes the page. Keep in mind what you want the reader’s eye to look at. You don’t want their eyes darting all over the page, which it will without proximity.