The Pocket Brush is one of my favorite tools, I highly recommend it to any student.
It’s a true brush, made with synthetic hairs that keep a good point for a long time. I’ve embedded a playlist of clips, including an intro and some basic instructions. More to come, and also see this section of Dynamic Drawing as well!
First thing you need to be mindful of is with a brush, we can’t feel it when the tip touches the page. We have to use our eyes instead. And it’s then the more we approach the paper’s surface, the thicker the line becomes. Practice trying to maintain thin lines for as long as you can, and then try alternating from thick to thin.
Then try feathering your lines, getting an even taper at the start and/or end of each line. Start with light strokes, then heavier, and finally heaviest. Try making brick like blocks, by bringing the brush down to a wide stroke immediately, and then lifting at the end vertically. The tear drop shapes seen in the sheet are made by drawing down towards the sheet quickly, like feathering but in a much shorter time.