On a wall.
Prominently, on the living room or dining room wall.
In the Hall as you enter the House.
Yes, this is where my aunt had hers. No one could miss it!
I don’t see them often in the US but in Ireland they were always in the front hall near the door.
Dining room wall was where my parents and grandparents hung them. Ours is in the breakfast area of our kitchen.
Not sure about tradition, but mine hangs over the fireplace in the living room. Our apartment is small, so the picture is visible from the front door and the dining area as well.
If it is part of the Enthronement of the Sacred Heart in the home, it is supposed to be hung in a prominent place.
Here’s an excerpt of a Letter of Approbation from Pope Pius XI to Fr. Mateo Crawley-Boevey, Ss.Cc., founder of the Enthronement movement:
We have read your letter with interest; also the documents that accompanied it. They give proof of the zealous and untiring labors with which you have devoted yourself, for many years, to the work of consecrating families to the Sacred Heart of Jesus in this particular manner: by placing an image or painting of the Sacred Heart in the most prominent place in the home, as on a throne, as a sign that Our Lord reigns visibly in these families. …]
Continue, then, beloved son, your labors and your apostolate, in order to enkindle the flames of love for the Sacred Heart of Jesus in Catholic families.