The Elements of Style

For quick reference, here are the 18 rules from The Elements of Style, by William Strunk, Jr.

Elementary Rules of Usage

1. Form the possessive singular of nouns with ‘s.
2. In a series of three or more terms with a single conjunction, use a comma after each term except the last.
3. Enclose parenthetic expressions between commas.
4. Place a comma before and or but introducing an independent clause.
5. Do not join independent clauses by a comma.
6. Do not break sentences in two.
7. A participial phrase at the beginning of a sentence must refer to the grammatical subject.
8. Divide words at line-ends, in accordance with their formation and pronunciation.

Elementary Principles of Composition

9. Make the paragraph the unit of composition: one paragraph to each topic.
10. As a rule, begin each paragraph with a topic sentence; end it in conformity with the beginning.
11. Use the active voice.
12. Put statements in positive form.
13. Omit needless words.
14. Avoid a succession of loose sentences.
15. Express co-ordinate ideas in similar form.
16. Keep related words together.
17. In summaries, keep to one tense.
18. Place the emphatic words of a sentence at the end.