Danny Gregory has a weekly “sketchbook club” video series on YouTube where he leafs through sketchbooks–his own or others’–and uses what he sees as a jumping off point for talking about sketching.
It looks like you already knew how to sketch at this time; I don’t know how to start.
Gregory, in responding, lays out a sort of “philosophy of sketching”:
I started this way: by carrying a sketchbook around, and recording what I saw in my life. That is how you start. Now you know.
He continues down this road, and by the time he’s done he’s described something that works well for sketching, but which is also a pretty good prescription for taking on anything new.
As someone who’s been carrying around a sketchbook in his back pocket for the last 4 months and recording what I see in my life, I can attest to this: there’s no better way to start seeing than by opening your eyes.