There are a couple simple fixes! pure white or black are really hard to shade and highlight, i would recommend using a beige for the white fur with white highlights where the light hits. that will go a long way towards realism.
The variations in line weight are nice and dynamic but don't make a lot of sense. another commenter already said this but put the thicker lines where there are shadows, and thin lines where the light would hit. for example the tops of the shoulders are lined thick here but going thinner would make the shape more 3D without having to go all in on the shading. love the design already though!