I randomly came across a frayed hardcover edition of this book as a young student about ten years ago and loved it so much that after extending the library loan 5 times I went on to photocopy the entire book (as it was out of print at the time and I was broke anyway). I still tend to think of it as instrumental in the development of my drawing, and am ecstatic it's available again!
Kaupelis' approach is to teach you how to truly engage with things as you draw them. In the beginning of the book he wants you to make marks in novel, fun and seemingly ridiculous ways (now commonly considered the 'right-brain' technique) that make you really look at/experience the subject you're drawing and dispel any notions of what might be a 'correct' representation thereof. He then focusses on aspects of shape, tone, composition etc. before moving on to abstraction and conceptual drawings.
His projects are consistently surprising, playful, adventurous and great fun (I thought), and you do see your drawing ability improve dramatically very quickly as you basically learn from yourself - you're bypassing received ideas and discovering something you've been able to do all along - before developing and shaping it. The 'discovering' part is especially exciting and inspiring as Kaupelis extensively illustrates his points using drawings by old masters, contemporary artists of the time and his own students, encouraging you to give your own work equal importance and learn from them as you would from peers.
Unlike the mass of books trying to teach people how to draw, it doesn't ask you to copy the author's style, to 'imagine things as cubes, cylinders and cones', to copy yet another tedious landscape or still life or supposedly 'proper' drawing. Instead, it wants you to experiment, to free yourself up as well as work hard on the classic elements that make up a great drawing. It's not a patronising 'quick fix guide for amateurs', but an invitation to take your work very seriously indeed while not taking yourself too seriously at all.
The fact that this book hails from the 70s (it's older than I am) might be a turnoff to some, but in my opinion doesn't matter in the slightest - even the later chapter about moving your drawing on and trying out new techhniques and technologies still applies.