The Elements of Style

by William Strunk Jr.

If two or more clauses, grammatically complete and not joined by a conjunction, are to form a single compound sentence, the proper mark of punctuation is a semicolon.

Oddly enough, this part helped me realize where I went wrong with commas and why I have trouble with them today. It's all to do with semicolons and the person who told me never to use them in works of fiction.