If you just want to draw or sketch having different grades for shading and tone then I would suggest either Faber-Castell 9000 Graphite pencils or Derwent Graphic Pencils, which are also Graphite. The grading of the pencils work that F would be the hardest down to HB which is the lowest of the hard scale; these are good for sharp hard or fine lines depending on how hard you press and would keep their points for longer. B to 8 or 9B are the softer range, the higher the number the softer the pencil; these tend to be used more for shading effects and work especially well on their sides. Both makes can be purchased as single pencils or a complete set. You will probably find that HB would be sufficiently hard enough for any drawing and from the soft range 2B, 4B, 6B and 8B or 2B, 5B, 7B and 9B

The Progresso pencils are really lovely to work with; being woodless graphite you can get lovely long points for shading, but they do only have five grades and are sold individually; HB is the hardest and 8B is the softest and I would suggest buying all five grades of these.