Rules I keep for type on screens

These are the defaults I start from when setting text for screens. I break them, but only when I know which one I am breaking and why.

1. Body text is at least 16 pixels, and usually more.
2. Line length stays under about seventy-five characters. Serif text can run a little longer, with a little more leading.
3. Line height grows with line length.
4. Two typefaces at most, and they must be clearly different.
5. Headings are closer to the text they introduce than to the text above them.
6. Never centre a paragraph longer than three lines.
7. Use real quotes and apostrophes, not straight ones.
8. Contrast is not a style choice. Check it.
9. Numbers in tables use tabular figures, so columns line up.
10. If you need a third weight, you probably need less emphasis instead.

The last rule is the one I break least. Most typographic trouble is too much emphasis, not too little.