I used to practice shading by drawing rocks, because the surface of a rock is very uneven so you get lots of different tones of shadow. Haven't doneany serious drawings lately...I did a quick pen drawing yesterday while in class (seeing ruins' pen drawing made me want to improve my skills
), I'll scan it and upload it later hehe.
Anyway, I think rocks are great for practicing shading, your bed sheets are also good for that (soft shading).

Anyway, I think rocks are great for practicing shading, your bed sheets are also good for that (soft shading).