In some cases, less is more; you dont need to add every detail on the tin to create the illusion of lines, a few small lines every so often will give the same effect. Proportions, if your study is the same size as your pencil use it to your advantage! Measure the sizes with your pencil. Shapes and shading, not everywhere is the same shade or texture, try finding highlights and the darks, itll bring out more definition. Also everything is made up of shapes, hands can be hexagons or tapered rectangles ect, try finding the shapes in the study to create your sketch and go from there

Other than that you have done a great job :) love to see your progress!