I had taken a series of sketching lessons a few years ago. I felt a lot of them were kinda vague and woolly, and it made me pass on making them a regular thing (that and the travel time was almost longer than the lessons themselves, on workday evenings).
I did like the lessons where you had to use your eyes (draw what you see, not how you interpret it), and the ones that dealt with shapes, shading and giving things texture and stuff. I’m still reaping the rewards of those today.