For me, it was: “If it’s going to help your players have more fun, cheat. Fudge a die roll. Make shit up. The dice don’t tell you what needs to happen, your players’ reactions do.”
Obviously, many people will disagree with this, but I’ve always appreciated this advice, and I believe it has made me a better GM.
@mr_noxx
“Only prep what is either absolutely necessary for the next session, or actually fun to prep.”
I get this one from Kevin Crawford. I find that it helps preventing prep from becoming a chore, and gives the nice long-term goal of making the “necessary” part of the Venn diagram as small as possible, and as overlapping with the “fun” part as possible.