Regarding the values, you just need to adjust the shadows a bit and emphasize the highlights while keeping the volume of the forms in mind, since the car currently looks a bit flat. I made some corrections by interpreting the shapes of the car and considering that the light is coming from the left side. Because of that, I increased the size of the cast shadow on the ground. As for the graphic style, I recommend using the lasso tool a lot. With it, you can draw the shape of the light or shadow and paint with strong, clean edges. You can also use a brush with some texture to paint inside the selected shape, which can create some interesting brush strokes. Try to soften certain areas where there is a transition between light and shadow to create a more appealing visual result. Also, look for references from artists you like who work in this style and study or imitate what they do. It’s a very good way to learn a technique. Hope this helps!
