Use numerals (1, 5, 653) instead of spelling out numbers in all but idiomatic usages, like "one in a million." If a number would thus be the first "word" in a sentence, try restructuring the sentence.

For large numbers, it's fine to use the abbreviated form (e.g., 40K for 40,000) in a headline or subhead, but use the whole numeral in body copy (e.g., 40,000 not 40K).

9 times out of 10, typography is the most important design element of a website.

Clear, concise