Not bad. Your lineart ist very clean, which is a good.
I'd, however, recommend you to take a look into real anatomy, especialy the skeletal structure.
For example, the heads seem to be rather unshaped, which may come from a lack of understanding of the skulls shape.
Also, be a bit more bold with the shading. Most of it is left in the safe "not too dark" reaches and makes most of the objects look flat. Don't be afraid of realy going all the way to really dark and saturate shades and shadows.
But for your very first digital drawings, they are definetly better than my first attempts. Keep practicing ;)