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.
This advice can be taken in various ways. My take is time goes by while your PCs are doing their thing.
Nefarious plans are carried out by evil minions and the latest exploits of your party of murder hobos has reached the next settlement. If your party does a side quest instead of saving the queen from a sacrificial ritual, they going to have more xp and gold but Orcus is now wearing a new queen skin loincloth.
Time drives the consequences of PC actions. The world continues on while your party is on their 6th long rest in a 5-room dungeon.