For me, learning how to draw anatomy was the result of practicing a lot, drawing both from memory and from reference. I frequently switched between the two so that my style would be a mix of realistic and cartoony. Unfortunately I can’t recommend any books for learning anatomy, since I never used these kinds of resources myself, but I definitely recommend doing gesture sketches from reference and from life whenever possible as a way to improve your anatomy skills. Speed sketches are a great way to learn: try to capture the overall shape and movement before going into detail, since this give your drawings more life.
