1. Spell out numbers of one or two words. Use figures for numbers of three or more words.*
Example: The syllabus lists three texts, one of which has 587 pages.
2. Do not start a sentence with a figure. Either write it out or rewrite the sentence.
Example: One hundred twenty-six pounds was what she weighed ten years ago.
Better: She weighed 126 pounds ten years ago.
3. Use figures for dates, addresses, percentages, fractions, money, divisions of books or plays, and time.
*Note: When to spell out numbers or when to use figures is changing rapidly, especially in journalism. Check with your instructor for his or her preference.