I can only share the things that worked throughout these few months of focusing on environments, and still learning more.
A. PERSPECTIVE
B. NOTAN
A. PERSPECTIVE
When you start understanding how perspective works, it becomes much easier to develop your own scenes. A good video that explains in simple terms what 1/2/3 point perspective is
1,2,3 Point Perspective by Alphonso Dunnn
And if you're interested in books you could check
Ernest Norling Perspective Made Simple
There is also Atmospheric perspective which you can find more info about in this video
Understanding Atmospheric Perspective by Scot Robbertson
B. NOTAN
This is essentially the exercises you keep seeing me repeat above, specifically the dark/white ones. What this allows you to do is find interesting composition/placements that works.
Could also be considered as thumbnail, which is finding ways to make a scene work. You can find more information about Notan here
Composition Design Notan
And of course, the other thing is to do mini-studies of photography/paintings etc. of landscapes, to find out what works, and play around with the piece you're studying from. Even better if you can sketch from real world interaction (plein-air) , but even though I say all of this, I am still learning and slowly applying what I just wrote here. Notan been one of them, and also overall structure of landscapes.
I am still exploring how to make landscapes work/interesting to look at, and what is interesting for me.
If you have any other questions let me know. Will try my best to answer, to the best of my current experience so far.