Spell out one through nine. Use numerals for 10 and above.
   There are three rules listed in this blog post.
   We will probably cover over 12 rules concerning number usage.

If a sentence or paragraph contains multiple numbers applying to the same category, treat them consistently. If one must use numerals, then all should use numerals.
   In three months, I presented 85 grammar posts and 5 non-grammar posts.

Spell out a number at the beginning of the sentence or rephrase the sentence.

   Two-hundred people attended the concert.
   The concert was attended by 250 people.