I promised pencil artist tips, didn't I?
Just finished a drawing using a charcoal pencil and it reminded me forcefully how careful you have to be with that beautifully black but touchy medium.
Unlike graphite your charcoal leaves loads of powder on the surface of your blacked-in area.
You blow it off and if you don't blow hard enough the powder just rests on the unused white paper and is the devil to get off. Even using your eraser can leave ugly streaks.
Of course you have to spray fixative when you have finished but be prepared to use a good few coats with a five-minute wait between. Boring but necessary. Test the blackest bit delicately with your finger and if it shows then do another coat until it doesn't!