Charcoal and pencil study of a sweet 7 week old puppy laying in the grass.
To achieve a rich dark black in a pencil study, without the reflective shine you get after layering several coats of pencil, I will often start with a charcoal or carbon pencil, which has a deep matt effect. Then I can put pencil on top. However, it doesn't work so well the other way around, as the charcoal doesn't "grip" so well. (the layers of graphite make a slippery surface) Not only does the charcoal easily build rich darks, but adds another texture to the drawing, making it more interessting than pencil alone.
I use paper tortillons (paper stumps), and sometimes brushes to blend, and push the pencil around. To remove and tidy up the drawing I use a regular rubber, cutting off pieces with a craft knife, so I can get into small areas and also a putty rubber. It's a gradual process of laying down the pencil/charcoal and then lifting and removing some of it with the various rubbers.
It is better to use a paper with some tooth, to grip the pencil/charcoal. Often I will use my sketch book for rough sketches, but for a finished drawing I prefer Fabriano 5 Hot pressed paper. It is fantastic to work on, and will take a lot of punishment (rubbing out).