This is similar to the way I work. Also, use erasers to work back into light. Clayboard is good of course, but a gessoed panel will do as well. Try charcoal next - it is not shiny like graphite, and the darks are much darker. Tip about charcoal: the powder does not work as well, it comes off too easy. A soft broad charcoal stick works good to just lay down some dark areas, then spray water and work it with your fingers. Another tip: use surgical gloves.
This is one of the pieces I uploaded: https://steemit.com/artzone/@thermoplastic/untitled-charcoal-1
For the signature: you can always add over top of fixative, then spray it again.