Nicolaides: The natural way to draw
I discovered this book with the promising title at Bookmans. The exercises are very helpful and this book provides exercises for different topics and techniques. I just needed to get this book and read through the instructions and tips. After spending 30 minutes in the store I decided to purchase it and I don't regret it.
I didn't have the time yet to read through everything but I already discovered a few interesting chapters. When I finish this book I will give some updated info on the main chapters and ideas. Meanwhile, I recommend reading this book by yourself when you're interested in drawing. I think a very good artist has a natural drawing skill with a unique style. Drawing is for me like breathing, like writing down ideas or simply a language. I needed to learn this language and find my drawing styles like every other illustrator and artist. This book can help to get an idea what natural drawings are and you can train drawing.
It is definitely an advantage when drawing appears naturally to you and you have a sense of forms, shades, and expressions. If you still struggle when drawing I do recommend to get a view of this book and read some helpful exercises you can practice.