Look before intervening.
The first impulse is often to change the thing that looks unfinished, unfashionable, or unfamiliar. Give yourself time to identify what it is. Good proportion and useful character do not always announce themselves in a listing photograph.
A mark is not a diagnosis.
Some surfaces need repair. Some need cleaning, some need specialist assessment, and some need to be left alone. Deciding which is which requires information, not just conviction.
Make the new part belong.
A replacement can be beautiful without pretending to be original. Think about scale, material, and the way it meets what remains. Matching every finish is not the only way to make a room feel coherent.
Let care be visible.
There is satisfaction in preserving a detail because you understood it, not because preservation is a visual trend. Keep a record of why you kept it. That decision is part of the project too.
The learning stays in the story. So does the useful part.
Make your own project brief