One of the most interesting yet challenging things to me is to get interesting shapes(a good design), when we are working in the workshops we do some things to see what each students particular struggle is, design value or color. We all struggle with one,my real tough one is shapes, color is my easiest. I wish it was reversed, why? Because people see the shapes first, and I have always tried to convince myself, that isn't true. It is amazing how we will avoid the truth, even when we know it. Abad design and the painting will almost always fail.
If you think you are good at shapes, do some value studies and redesign the shapes several times, try to paint an interesting tree, rock pile, or set of clouds. Make them up if you are used to copying from photos. High level artists seem to paint in shapes from shadow, light and mid tones, so subject matter becomes almost irrelevant, that keeps everything exciting no matter what you are painting. Which keeps you motivated, thus painting, thus you are always getting better.
Here is a painting I painted a while back. because I love yellow trees. I would change a few things now( mostly shapes), but I would do that in all my paintings. Be grateful you can see the changes you would make now and don't cringe at your earlier paintings. Revel in your learning. Heading to teach in St Simons, the plein air season really begins, exciting.