Doctor Whooves

Your pony drawing is great, good perspective on limb placement and overlap. Compositionally, this is pretty solid. I'm not crazy about the additional shadow behind the Tardis… it seems a little unnecessary, same with the shadow to the left of your pony. Remember, shadows tell the viewer where the light is in real space. According to your shadows there are 3 light sources, generally when it comes to shadows, we pretend there's one. The other thing I would recommend you concentrate on is LINE QUALITY. I'm not yelling, just stressing how important good line quality is in illustration. The entire line is the same thickness throughout, that tends to be visually boring. There are few artists that use it with effect, but they are definitely the exception. Start your lines thin, let them grow and shrink in thickness depending on what story that part of the drawing is trying to tell. Bottom of the hooves? Thicker. Top of the nose? Thinner. Thicker lines on the bottom can reinforce a sense of weight in your drawing. If there was one thing I wish someone had explained to me when I started, it would be the importance of line quality. Or heck, even what it was! A few places where the line should be smooth, it's a little shaky. Make those strokes faster and it will help smooth them out.