Seems like an obvious question - bright enough! But if there is a brightness which best gives a sense of reality, that doesn't necessarily imply it's best for our image. This is an opportunity to be creative. In the old and darken days, one could simply adjust the exposure under the enlarger and prints that were muddy dark or weakly pale were all too common.
With computer editing, it's much easier to nail the white and dark points via your raw converter or levels or curves in Photoshop. this means that a really bad print is harder to achieve, though not impossible.
There are times that a particularly dark print looks out of place, but often it can be very effective for creating a mood, especially when parts of the image are maintained, while other areas are driven a lot darker. Done well it looks natural if not reminiscent of the scene and can turn ordinary into great.
Likewise it's possible to make a really light print without looking washed out, giving a sense of the light flooding the subject. It has to be done well and doesn't suit all subjects, but can be just as powerful a tool.
What about trying some high and low key printing of your own on previously "normal" images. You might just like what you get.