Layout (Developed 2)

This is the developed version of my previous layouts.

I had a class show & Tell and I have got very good advices of what I can improve on this layouts. Firstly the layers are not working. Over lapping too much and hard to tell whether it is a tree or a mountain behind the front tree. Secondly the shadow is too harsh, especially the shadow on the right hand side. Wrong shape, I got to think about where the lights are comming from. And lastly, I got to think about using a brush that is more solid rather than painting style.
After the advice I felt like I have A LOT of work to do... to improve my Layouts. I know what to do, but I am struggling to get on to it and do, I don't know where to start!! I may have to re-design my layouts and start again from scratch.