Yo. I'm enjoying watching your progress. I agree, if you're using the retractable pencil pictured, I'd invest in some softer/darker lead. Any and all exercises could be beneficial now. I'd be thinking about economy of mark making. The neck on your self portrait is covered in marks that aren't descriptive, there must have been some variation in tonal value there. I'd look at cross hatching too, I find it keeps the pencil active, and you're less inclined to follow a 'line' you think is there. Let the viewer's eyes fill in the blanks.
The Andrew Loomis books are great.