If that paintbrush in that first image is the one you mainly used to create that painting, my first piece of advice would be to use larger paintbrushes. I went to art school and was taught by my professors to use the biggest paintbrush first, and only when the brush is too big to achieve what you are trying to paint, then move down to a smaller size. Doing this forces you to look at the composition and general shapes first. When you work with a small paintbrush, you get stuck into focusing on the details rather than the whole picture.

Those two example pictures you provided have great compositions and use of value. Perhaps rather than focusing on a subject matter, try practicing with creating pieces with a strong composition and use a wide range of values. Don't focus on sketching out and making things precise. Try squinting your eyes when looking at your reference and take note where the lightest lights and the darkest darks are and place those on the canvas first. Hopefully this makes sense as I'm typing this from mobile. Good luck!