The line between legal and illegal isn't fixed, and can come out and grab you : I often hear the voice of my business ethics prof Dr. Windsor when I read about all the shenanigans at Enron, Worldcomm, Parmalat, etc. and did a post on his advice before. Although appropriate, Dr. Windsor never referred to me as "Young Grasshopper".
Never ask a man how much he makes or how many women he's made love to: I think Dad was trying to tell me that there are just some things that should always remain private.
Automatically put aside money from each paycheck into savings so you never see it in your account: Mom's a CPA. Enough said.
Don't go outside with a wet head!: My grandmother, rest her soul, was chock full of wisdom on how to avoid getting sick, what to do when you got sick, what to do when you were no longer sick and how to avoid getting sick again. She lived to 86.
Don't put your #$*% where you wouldn't put your tongue - Dr. Bessem was a gynecologist and my friend's father, and he would sometimes come into the gameroom where we were hanging out, scotch in hand, and dispense all sorts of interesting advice that was probably more appropriate to a hormone-raging 17 year old than grandma's advice.
Interested People are Interesting People - I spent 6 years at summer camp as camper and counselor and we always had a "thought of the day". Most were trite truisms we have all heard before. Sunday was always a Bible verse. But a few stuck in my head that were valuable as I grew up and entered the business world, like this one. This is similar to "People's favorite subject is themselves", and whether on a date or doing sales, this is good advice.
I have a bunch more, but a blogger friend of mine told me to always keep my posts short to keep them interesting.