Hardest rule to follow

Vonnegut's "How to Write with Style", list rules that you should follow to be a successful writer. The hardest rule to follow for me would be to "say what you mean to say/sound like yourself". It is going to be difficult to do for me because I use slang and a different vernacular than most because of my upbringing. I tend to use filler words and repeat things a lot. This makes it hard for me to get my thoughts on to the page in an intelligent matter.