Le secret d’ennuyer est celui de tout dire
The secret of being a bore is to tell everything.
Sept Discours en Vers sur l’Homme (not my translation; found on GoodReads).
One tip for good writing is always to show, not to tell, what you want to say.
I quite like it when a writer merely hints at the truth of the tale. When they hope that the reader has some intelligence and can put two and two together. When not all of the threads of the story are knotted and neatly tied up when the writer says The End.
One “rule” for dating is to leave [the person] wanting more. I think the same can be said of the relationship between writer and reader. Even with a stand-alone novel, with no planned sequel, I think there should be something left open, for the reader to wonder about. Not necessarily anything major, but something. Some little niggle that leaves you wondering.