Not exactly a full tutorial but this is pretty much the gist of it. Only leave the important lines or the ones that suggest shape depending on how much you want to simplify it.
This really depends on how realistic you want to draw. I recommend learning anatomy then simplifying just so you know how all the muscles, joints work etc. This will give you a better understanding of making poses and anatomy look more convincing.
Thank you this is really helpfull and convienent, i bet you just helped a lot of artist's! But i would like to point out that the front view of your muscle-y body here has the neck too small for the shoulders or vice versa, just a little critique that's all