Train your replacement before you leave. Leaving a mess behind erases half of what you built.

Anything that only works because you are there stops working when you go, and what people remember afterwards is the gap rather than the years. Handing over properly is unglamorous and slow: writing things down, introducing people, letting someone else do it badly while you are still around to help. It is also the part that decides whether any of it lasts.

Name your successor early, even informally, and let them run things while you are still there to catch problems. Write down what only you know. Judge your time by what survives a month after you leave.