2014 update: This is quite old but hopefully may still be helpful! Remember to reference a bunch of different tutorials. I honestly didn't know a whole lot when I made this so it's very surface level. BUT if it's any help I'm very glad! Now go study from some photos and such! Also, recommended reading is James Gurney "Color and Light".
Due to popular demand.... here's a shading tutorial!
-This is just one guide! There are many other useful tutorials out there that go into more detail about certain points!
-Remember to learn about shading and lighting from photos and not just from art and tutorials. Don't copy other people's mistakes!
-I am not by any means a master of any of this... remember that you're the one choosing to follow my tutorial, if you do haha!
With that said.... ENJOY!
Also, I've created a Supplement:
And please view part two!
OLD Tutorial on Multiply Layers: