yes exactly! Thank you! 
Hey, last artwork is really nice, but and really muddy. Try to use more solid brush, even without transparency and focus on solid shapes and just after that add light and shadow. When You add shadows and lights try to keep your tonal scale very simple and limited, because now You're using palette like almost from black to white on same object and it start to look too noisy, fractional and unreadable. If you solve this muddiness - you'll become awesome! 
Thank you, @dvlfsh that was really helpfull, very clear advise!
so today I just did studies from reference to get values better in my memory library
I think you should use also hard brushes for these studies for more believable results. Also try to copy (or just analyze) photos of real primitives from gypsum. All those soft reflections, subtle smoothness of edges, balance between crisp and soft, etc. Devil in the details! 
Yes, it really looks weird with the softbrush, I still have to figure out when to use which brush...thanks for the link, I was trying from real life but the values on those photos seem more clearer so I will try that. I read your post after I did my stuff today but I take your words for the next studies. I am not proud of those especially for the little amount that I can do in one day because I am really slow, but I told myself that I will post something even when it sucks 
Good mindset, keep trying!
I'm, not sure if it helps with your problem, but hope it will. 
Blending techniques: Part 1, Part 2, Part 3
Little bit about theory and terminology: Shading Light and Form
Also you could start with flat shapes of all shading elements from Proko's video and then mix them with techniques from CtrlPaint's tutorials. It's good exercise too.
Keeping my eye on this blog, studies and exercises are the quickest ways to improve, and you seem to be doing them. =)
Thank you for the example, @shiv0r. The links are really usefull, @dvlfsh thank you too! That´s really motivating, @stealcase 
Ok so I tried out the smudgetool and the mixerbrush. I found a way to get in the direction I wanted. During rendering I already noticed that the shadow is too low but I kept going because the effect was in that moment more important for me. So it probably doesn´t make a lot of sense but I learnt sth, so I will keep the thing I did wrong in mind for next studies. I think there is a lack of valuedifference too what makes the form less readable, well, next time 
that was the reference I was working from: 
