For the shoulders, draw a mental picture of what they look like under the clothes. Better yet, take off your shirt and do a study. I'm seeing a very large radius for the outside curve. It's hard to picture shoulders being that rounded.
I highly recommend Tony Ryder's book. His system is very methodical. He eliminates all rounded lines from the initial stages of the drawing. Using straight lines, he sculpts away at the figure until an accurate drawing emerges. It's not magic. You still have to use your powers of observation. But it's easier to position simple shapes, then refine them into a more complex ones.
Go to
www.tonyryder.com to see his drawing demonstrations.
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