To achieve a better balance between light and dark tones I recommend two pencils; the 2B that has a softer mine, that is, leaves more graphite on the sheet and we get darker tones . And the 2H that has a harder mine so lighter tones are obtained .
Now I will explain the exercise that will help you improve the transition between light and dark.
STEP 1. On a sheet of paper, draw five boxes and paint the gradient values from pure white (we don't paint anything) to dark black (greater force on the pencil). The purpose is to gain mastery to represent different values of darkness.
STEP 2. To begin with, use only the HB pencil, which is the basic pencil. Once you have exercised well try 2B, and then with 2H; and finally when you have mastered the practice technique with all three at once.
This practice with the three pencils separately will allow you in addition to a better handling of the varieties of tone, you will know with which pencil you can achieve a better tone and thus give a better finish to your drawings.
Another important aspect to know when drawing are the types of lights and shadows that can be represented in a drawing, this I will explain more fully in the next section.