The Beauty of KNOWING what you ARE doing.
The book is highly recommended. Furthermore, (what most people forget to say) I highly recommend you to USE it, too. If you want your life to make sense at some point you know what to do. Either that or come up with a better book to surprise the world.
First Attempts finding proportion -
Note : You'll realize there are several drawings of the same thing. Believe me, THAT is the POINT.
I was about to commit the great mistake of just showing ONE example out of all my trials, but then where is the point?
Eureka! ---Now, THAT is surprisingly proportional (just in case you can't read my drawing)
Which means your brain finally knows how to draw a figure exact enough to draw it again and again and it will be proportionally CORRECT. Do not try to skip this step, though! In other words, Do not try to DRAW my drawings!! You got to draw as many as I drew (and I had plenty more but that is surely enough for you to get it, I hope!) and the more you draw the more accurate.
Think this way: "the more you try to draw exact, the more exact you will draw"
(Simple, huh? -Now Just Do it!)