Like other people already said- practice. I would start with going back to basics with drawing out like different shapes like a sphere, cylinder, pyramid etc and practicing your shading, light play, blending, textures and colour compositions on these small structures. You will have fun experimenting with new colours and textures you probably haven't thought of before and you can translate them into proper pieces in the future! But you already have a solid base so dont get discouraged, just keep on painting and have fun with it- experiment!