Always remember to use sandpaper sharp pencils in the rendering stage.
Mechanical pencils saves a lot of time - you don't have to cut them, only sharpen with sandpaper. And you can control the length of the graphite.
If you tilt the pencil too much, draw flat, then it won't give up so precice tone. If you hold it closer to 90 degree angle to the paper it goes into the paper much better.
Some use long-haired brushes a lot. But it's not that necessary to use brush in the lights if rendering the lights with the 2H(you did the rendering great btw).
What they do(personally I don't like that way) is that they kinda draw with the brush - dip the brush in a bit of graphite and just draw with that on the paper! It's very fast when you're good at it, but I find it too imprecise to even start working like that.
Just experiment and you'd find your own way!
I'm sure you've been through Dorian's excellent Bargue tutorials?