While writing the lessons for the Typography module in my upcoming Shift Nudge course, I came across this little gem in "Elements of Typographic Style," a book by Robert Bringhurst.

...a (type) face of modest merits should be handled with great discretion, formality, and care. It should be set in modest sizes (better yet, in one size only) with the caps well spaced, the lines well leaded, and the lower case well fitted and modestly kerned. The line length should be optimal and the page impeccably proportioned. In short, the typography should be richly and superbly ordinary, so that attention is drawn to the quality of the composition, not to the individual letterforms.