Rule No 1 that I never break: I always close my rotary cutter after each cut. I never cut with the rotary cutter without a safety device for my fingers.
I wear shoes in my sewing room and when I'm sewing. I will not sew over pins. I don't pull my thread from the machine from the top, always from the needle. I won't use old bobbins. I guess these are my only do or don't sew at all rules I have for myself. Other rules are made up as I go or broken.