“Cows die,
Family die,
You will die the same way.
I know only one thing
That never dies:
The reputation of the one who’s died.”
-Hávamál 77
Together with verse 76, which is much the same, this is the most famous part of the Havamal. 76 starts the same and says that “a good reputation never dies, for the one who earns it well,” but I prefer this verse. It implies that the reputation you have earned at your death is the one that will stick around, whether good or bad.
The advice, then, is to work on that reputation while you have time to do so. Leaving a good legacy is more than doing one good deed, it's continuing to be a good person as you grow and change with life.
I think this also applies to remembering those who have passed. Odin wouldn’t say, “Don’t speak ill of the dead.” Everyone should be remembered as they lived, even if they were an asshole, and it’s okay to say so.