In general spell out numbers one through nine. Use numerals for numbers 10 and above.
Delete th, st, nd, and rd when working with numbers: June 1 is correct vs. June 1st
When “th” or “st” must be included, do not use superscript: June 1st is correct vs. June 1st.
Avoid beginning sentences with numbers. When unavoidable, spell out all numbers that start a sentence, except when a year or numeral and letter combinations begin the sentence: 2010 was a great year. 3D movies are fun to watch
Use numerals to indicate age.
Use numerals for dimensions, but spell out the unit of measure: 6 feet, 3 inches
Use numerals to indicate speed.
Use numerals when writing percentages or millions of dollars.
Use the word “percent” instead of the symbol.
School years should be written with both full years separated by an en dash: 2012–2013