He means that the lines are very choppy/not straight. The whole piece is very random. You have a different style for every letter. The 3D on the letters is different for every letter. When you're trying to make letters look 3D, make sure the depth is roughly the same for each letter. As for the backdrop, the colors are too varied and not opaque enough. When drawing graffiti, you want to make it look like it's spray-painted. I'd recommend using Sharpies or making sure your colored pencil is as opaque as you can make it.