You have beautiful rendering, with great control of light and shadow. I think the thing to focus on next is the underlying structure of what you are observing, so being able to draw out the objects with correct perspective. Take some time to study breaking down objects into their most basic forms, such as spheres, cylinders, cones, and boxes. This video goes more in depth and I think you'll find it helpful: https://www.proko.com/s/sZsC. Having a solid drawing foundation is key to a good illustration, and practicing it more specifically at the level of basic forms will help you improve much faster. If you are also interested in portraiture, reviewing the Loomis model, a method of breaking the head down into simpler forms, is also worth checking out: https://www.proko.com/s/1cX2. Hope this helps!