Drawing on the Right Side of the Brain: The Definitive, 4th Edition
https://read.amazon.com/kp/embed?asin=B005GSYXU4&preview=new...
This is probably the best book I have come across and it took me from stick figures to what my family considers awesome in about a year.
[Edit]. Also, drawing people is a really good test. If you draw a house or a tree, say, you can get the shapes / proportions wrong but the thing might still look plausible. Draw a head out of proportion, though, and it will immediately look wrong.
First is the exercise of drawing the "column / two-faces" drawing. You can REALLY feel your two brain sides fighting while drawing that.
The second is the "upside down" drawing. After I finished that I was amazed that I actually had drawn that (I cannot draw a cup or a house or whatever).
The premise is that a lot of people who have the "left" side of the brain developed draw the "concepts" of what they see and they don't really draw what they see. So if someone tells me to "draw that house", I will be drawing "a roof", "a door" , "the walls" etc. Instead someone using the "right" side of the brain will actually see the house and draw what they see.
Pretty clever.
For constructing energetic characters, I like the Marvel/stick figure approach of "How to Draw Comics the Marvel Way," by Stan Lee and John Buscema (also John Romita's book "Draw the Marvel Comics Super Heroes", which is sadly out of print but not hard to track down.)
Note that these books concentrate mainly on line drawing. Shading (or inking and coloring on the comic side) is of primary importance for turning line art into three dimensional art, and I don't have a great reference off the top of my head.
I think drawing programs with perspective grids can help as well. And lots of people use 3D software as a composition aid or to actually draw on top of. Some consider it "cheating" but remember that the old masters used optical devices like the camera obscura and wire grids (known in antiquity) as well as Renaissance optics like lenses and mirrors. I believe David Hockney tried to replicate some of these techniques with much success.
It is easy to lose focus when drawing. Hang in there. Look more closely. Focus on the details. Try to copy as much details as you can.
The quote "Good artist copy great artist steal" is true in the sense that the more we focus our attention on the details of the drawing the closer we get to copy/literally steal the feel of object we're drawing.
I can't open that link.
Drawing on the Right Side of the Brain: The Definitive, 4th Edition
https://www.drawright.com/before-after
Incredible results for only six days.
Get this book, go through it, then look into drawabox if you are looking to draw from life.
For constructivist illustrations or styles like manga, I'm still learning.