I'm not specifically learning to draw right now but I do love how Ralph Ammer builds his lessons. Split into short exercises, the best parts are the animations he draws and integrates in his lessons as gifs. Much lighter and more pleasant to watch than a video, they are very short and looping so you can easily grasp what he's explaining. Here are a few images from his most recent lesson.
Dynamic drawing:
Rotating cube and vanishing points:
Perspective: