These are very clean, good work. But I feel that your drawings are a bit stiff. Try using more curves.

Well done Yuri! Those are really good! With these few plans you can easily guess the environment you have in mind.

So, the trick is to try to ignore them. Look for landmarks in the skeleton. For example, figure three, you clearly see the clavicles, the rib cage so you're seeing it from above, not from below as you drew it. By changing the perspective that crease that confused you makes sense; the torso is rotating and so are the muscles and skin, following the ribcage. 4 is right, those parts are in perspective, as is 5 where you see the top of the ribcage.

You could give advices only when you are sure, it's ok. But in other cases you also can share your opinion (just say that it's not advice, just your point of view). If you are wrong, someone (maybe author) will correct you. It will be very useful for you. For learning english try "Basu". Very interesting app with different exercises. Also "Tandem" is cool app for talking/chatting with native speakers. I use both