Value drawing is like painting in graphite, and although the process is different to using a brush, you need to think in terms of areas as opposed to lines. Shade the darks, observing the shape and value, shading carefully up to the edge of adjoining light areas. The astounding realism that we see in some images is this approach taken to a very high degree of detail, where the tonal values are closely observed and finely drawn.
In the example shown here, a detail from a still-life study, a glass of wine provides interesting reflections and highlights. Sometimes it can seem odd, drawing strange shapes across the smooth surface, or light value when you know the wine is dark, or letting the edge vanish against the background when you want to draw a line; but if you trust your eyes and try to capture what you see, a realistic drawing will emerge.
Tools for the Job:
An H pencil should be as hard as you need for lightest tones; an HB will give you a good mid range, with B and 2B for darker shades. For very dark areas a 4 or 6 B might be needed.
Using the Pencil:
Keep your pencils sharp, and apply the tone with small rapid circular or sideways movement of the hand. Randomly varying the stopping/starting point of the shading will help avoid unwanted bands running through an area of shading. Use a slightly harder pencil to work back over an area done with a soft pencil, to even out the tone and fill the tooth of the paper. This also reduced the contrast in texture betweeen the various grades of pencil. An eraser can be used to lift off highlights. I recommend that beginners avoid blending or smudging at first, but rather learn to get the most out of the pencil mark. Once you are confident with your shading, you might like to try using a paper stump to blend tones. Make sure you use a full range of tone - many beginners are afraid of dark tones, or jump from light to dark but miss the in-between steps.