Never say anything in writing that you wouldn't comfortably say in conversation. Be yourself when you write. If you're not a person who says 'indeed' or 'moreover,' or who calls someone an individual ('he's a fine individual'), please don't write it.
William ZinsserWriting is such lonely work that I try to keep myself cheered up. If something strikes me as funny in the act of writing, I throw it in just to amuse myself. If I think it's funny I assume a few other people will find it funny, and that seems to me to be a good day's work.
William Zinsser