Revelle Humanities Grammar Handbook
6 Sentence fragments
7 Run-on sentences
8 Verb agreement
13 Passive voice
15 ESL
17 Misplaced modifiers
18 Pronoun reference
20a Comparisons
21 Parallel construction
23 Commas
23d Sexist language
25/6 Semicolons & colons
29 Ellipsis
31 Brackets
35 Apostrophes
36 Abbreviations
37 Underlining
39 Numbers
41b Slang
41e Jargon
41f Pretentious language
42c Idioms
42e Clichés
43a Fluff

39 Numbers
Generally, the rule is: spell out numbers that are two words or less, and use numerals for numbers that require three or more words.

Example: While over 100 sailors left Troy with Odysseus, only one returned to Ithaka, Odysseus himself.