Hello all! I'm new to pixel art, and what I was wondering - what is the best way to learn the art of shading? Are there any step-by-step examples or anything? Thanks for taking the time to answer this

use references photos..
when you aer going to draw/make something you can look out in Google for a reference photo from what you are drawing (dog for example) and you can try to move the shading to other places for practicing

in this example you can see how light hits an object.., how light isn't there (object over it that blocks light [arm]) you can see how a shadow is made..
this may not be the best example but you can learn from it. but i assume this isn't what you are looking for.. so.. actually there isn't a best way to shade is just matter of practice so you can try to master one technic of shading or the one that you most like.. or it's easier for you and looks good.. just go and look some tutorials of how to shade a ball like hatch said so you can apply that..

Also, as a side note, the amound of midtones in your colors help define the surface reflective ness. Materials such as rubber or wood have more midtones, materials like plastic and glass are very reflective and have less.