For more detailed information and examples, please see The Associated Press Stylebook (55th edition). Numbers are discussed on pages 6 and 212-215, among others.
Use first though ninth in street addresses.
The shop is located on First Street. Or is it on Ninth Street?
No, I'm certain it was on 10th Street. The complete address is 205 10th St.
Generally, spell out one through nine, but use numerals for 10 and up.
There were five dogs chasing two cats, and the 10 staff members were trying to catch all of them.
The two cats were chasing at least 15 mice.
Pregnancy is a very long nine months.
Use numbers for one through nine when using hyphens to create an adjective before a noun.
The 8-year-old child through a temper tantrum as if he were two years old.