well then here is my tip in case you don't know yet..
tools needed:

• pencil sharpener
• a pencil

technique:
rotate the tip of the pencil against the razor untill you get a fine graphite powder

play with it :)

this is great for soft shadows and noises..the more you press it with your finger the more dense will the shades be and viceversa

this is one of many techniques that I find fun to use but be ware this can eat away ur pencil :p
enjoy