Grammarcheck.net recently posted this infographic of 21 frequently ignored (or unknown) grammar rules and writing mistakes that everyone who writes should know.
How many do you know? How many do you ignore?
I’m with them on all but the serial comma and semicolon. I only use a serial comma for clarity in my writing. And, I think the semicolon is too formal for my voice. I only add it when my copy editor insists.