Skip buying the whole pack of pencils when you can get all the shades you need with just these 3 pencils!
 
2H - Hard lead, lightest shade.
Used for refining and fine detail.
Bad for drawing outlines and scaring paper.
 
2B - Softer lead, medium is shade.
Used for outlines and shading lighter values.
Bad for dark values.
 
8B - Softest lead, darkest shade.
Used for dark shading and softer textures.
Bad for smudging and fine detail.
 
Shading is all about getting a range of values so the contrast is high. These 3 pencils cover all of them. Practise your value scale using each of these pencils and you can see for yourself what they all do!