Mild to moderate pressure is probably better. If you use heavy pressure, you will indent the paper and you will not be able to remove the impression. If you need it to be darker, change to a darker (B) pencil. You are shading in multiple directions, which you can do, but it can make it look unclean if it is not blended well. If you think about light, it has a consistent and pretty uniform effect, whether that is causing light or shadow. However, the overall effort is still good, keep practicing.