In my search to learn how to draw, there’s a particular set of books that I picked up a while back and that I think anyone should have, if they want to improve their skills: the Andrew Loomis manuals.
Andrew Loomis was an illustrator from the early 20th century, and his manuals are still in print today – and still available online in PDF format, as they’re out of copyright in some countries. They are, in my opinion, a complete guide to drawing well, especially figure drawing, in spite of their old-fashioned style. Loomis was a professional illustrator above all else, engaged in the practical craft of commercial art, and not art for art’s sake.
Of course, any artist would be well served by learning the basis of good drawing. After all, we have to know the rules to break them effectively.
Loomis is notable for how readable he is, even all these years later. He was a teacher, and focused on doing art well as much as doing it at all. His books make you want to draw, even though you might not be good at it. He seems to come with the promise of getting better at it over time.
If you’ve never heard of him before, start with Figure Drawing For All It’s Worth. You won’t regret it.