List three things that you can't draw at ALL

[Chutzpar]

The more I think about it, the less I like the idea of identifying specific objects or situations that you can't draw. It's better to think in terms of principles.

I'm not picking on you specifically, Lexou, but using your post as an example, these:

1. Top viewed poeople. HOW LONG IS A NOSE AND DO EYES SHOW
2. Bottom viewed people. HOW LONG IS A CHIN

Are essentially the same problem, and would be fixed by practicing the same things; that is, establishing the head as a 3D form and really focusing on how you place the features on it. The same really applies to the whole body; break things down into simple shapes and then worry about detail only once you've got the construction as tight as possible. Once you understand the body as a series of simpler shapes, it takes a lot of the pain out of perspective and foreshortening
It still takes a lot of practice (I STILL SUCK AT THIS A WHOLE LOT), but it gives you a stronger foundation to work on c:

Also, for this:

5. Pretty, unique and different adult women.
6. Ugly, yet feminine women.

DRAW FROM LIFE DRAW FROM LIFE DRAW FROM LIFE DRAW FROM LIFE.
Go to a coffee shop or a cafe or something and do caricatures and sketches and whatever else based on people around you. It's... morally questionable to draw people without their permission, but basically every artist ever does this. Again, look for basic shapes in people's bodies and faces.
If you don't feel brave enough to draw strangers, then draw friends and relatives and teachers and anyone else you're willing to ask! You'll start noticing all kinds of variations with people eventually, and applying them to your own drawings~
Also check out this drawing and the description because Buuya is amazing:
http://buuya.deviantart.com/gallery/#/d2z6syz