Today my block-in was stronger because I used a technique I saw in a DaVinci Initiative video, where you draw in angles with follow-through lines. The idea is that by continuing the line far past the section you actually need it all the way to the outer parameter lines of the subject, you get a more accurate angle because you can compare the negative shapes and alignment in relationship to other angles. I was surprised how helpful this was for me! I also remembered to work with more plumb lines which helped a lot.
Since I wanted this to be a quick 15-minute sketch, I didn’t concern myself with every fold and shadow — just enough to suggest that the dish towel was folded over on itself. I used the 2H lead to block the towel in, then emphasized some edges and darker values with a 2B mechanical pencil.
One thing I could incorporate next time is to notice early on where the horizontal and vertical center lines are in the subject and make note of them on the sketch for more reference points and orientation.