Black and white are polar opposites as tones. Even in color photography, they are the exact opposites of each other, and are added to induce more of a dramatic feel in the photos. In black and white photography, they are once again the opposites; only this time they are all that your eye will see. There are however, other parts of the image that are very important in grayscale imagery; the grays.
Grays have several purposes in monochrome, chief among which is the role of a subtle bridge between the sharp contrasts. The amount of gray in an image can differ, with the least being added in dynamic monochrome, and the most in portraits and softer landscapes, such as those involving fog or misty areas.
A very popular technique in monochrome photography is to capture a broad range of tones, with multiple shades of gray in between. This serves to soften the image a bit, the ideal scenario for a gentler image that is not meant to be very striking. Shooting portraits, especially small children, is the ideal practice with a wide tonal range.
For softer tones, you can either shoot in places with a natural haze or fog, or artificially induce some, whether in person or through editing.
The best black and white photos, by and large, are the ones that exploit the tonal differences the most. While each photographer has their own preference as to how they like their black and white photography, it is important to explore and find out for yourself, how you like to express.
As always, it is very important to shoot in RAW, as black and white photos have the most room for editing. This is because of the fact that even though they are expressions unto themselves, they are somewhat blank canvases as well. As far as tones go, you can always increase of decrease the dark or light tones present in the image via editing software. You can also add mist, as mentioned, for a considerably softer image with a smoky finish.