You're really doing good. I was also stuck at improving, but learning about different artists and watch their tutorials helped me in every way like playing with colors, making the painting look so much fun(I recommend Marco Bucci), studying perspectives, compositions and anatomy(David Finch). When I discovered these people, I was drawing for 2 straight days, I just cant stop haha.

These are really good, but it seems like you have issues with the same kind of stuff I struggle to get bettar at. My thoughts are mostly about getting different textures and surfaces across. Most of my digital work feels a bit glossy or waxy if that makes any sense. One of the keys to get it right I my opinion is to work with different levels of contrast depending on the reflectiveness of each material. Skin can be quite reflective, bit it can also be quite dull depending on the light. Hair is often pretty shiny and it often works well with higher contrast. You really got the shiny fabric of the clothes on the second picture across. Keep up the good work buddy ^^

maybe you can add a another layer on top, set it to a different blend mode and add some details or highlights. This small effects may add some intersting touches.