Learn how to sharpen and hold a pencil properly(watch all 4 videos), learn about values and edges and the laws of light, gesture (1, 2 structure, then you will need also anatomy (some good books are: Stephen Peck, Goldfinger, Bridgman, Hogarth, etc.). Copy and study from your favorite artists, and especially the old masters (guys Michelangelo, Tiepolo, Prudhon, Boucher, Rubens, Watteau, etc. amazing draftsmen and anatomists. But study the guys you like, I like Fechin and Repin a lot). That´s pretty much it, values are one of the most important things you can learn, they are constant across media, whether you are drawing with pen, charcoal, oil or gouache or digital, so are edges. Some books that are based on this drawing system (which is really the classical way of drawing, coming back to Florence and Michelangelo) are Vilppu Drawing Manual, Michael Hampton Figure Drawing Design and Invention, or the one by Steve Huston.