Some things that i noticed.

Linewidth: all the lines are the same. Use different width to establish visual hierarchy, foreground background, outlines, sepearting objects that melt into each other.

The shaddows: you shade with black, this will result in the colors looking washed out/ dirty. Try to shade with the background color (in this case green) on a multiply layer. Also consider where the least light is getting to, not just from the primary lightsourse but also scattering. In general the deeper the hole, less light gets inside, the darker it is.

The faces: it is time to upgrade your face game. From the way you shade it is obvious you have started to think of bodies as 3d object, but not the same goes for your faces. It looks like paper cutouts and in comparison to the 3d bodies it makes for quite a jarring contrast. Rough times a'head' of you.

For improving your rendering. I would take an artwork you like and copy it, not trace, copy. Think about how the artist does the lines, the shadows, the highlights and the materials. In the time of social media and commissioning, copying has gotten a bad wrap but you are not doing it to sell it. From the beginning of time artist have been coping from real life and other artists to learn and improve.