There are lots of different ways to shade but I'll tell you how I shade. There are examples in my gallery if you wanna check them out #Echo :3
Anyways, the most important thing about shading is imagining a light source, then all the shadows will be on the opposite side. Its probally best if you just use one colour for each bit you wanna shade. To get a good tone, select the original colour of the bit you wanna shade then sorta move the cursor on the colour select thingy diagonally. You are aiming for a colour that looks the same but it has more black in it.
I also add extra shading on the hair and eyes by creating a gradiant on a new layer. This is a little harder but its actually really simple but looks awesome. To create a gradient and select black and make its opacity to as light as I can. Then a draw over the part I wanna shade. I keep doing that over and over to bu ild up a gradient. Then I just erase the bits I dont want and then merge the layers.
I hope this all makes sence and helps and stuff, its kinda long and im not very good at explaining stuffs DX So yeh see ya :3

keep practicing! iv got some pics that might help with learning how to shade so if you get the chance check them out :) i hope i can help

@Echo Project
Thank you so much!It's really helping me!^w^ I'll look at #Echo also

@maxymash27
I'll have a look ^w^

The best is watching replay of how did other people, good luck, and never give up XD

Thanks :3 Its nice to be appreciated, also Ill be sure to look at more of your artwork when you improve :3

wish i could i help, but i suck too
and the whole light thing is pretty confusing to me -_-'''

Well, the easiest way to shade is to color your hair one color, then lighten the color, use an airbrush, and make a line going through the middle of the hairpiece. For clothes, use basic shading, as if a light was directly above them. If you are confused search @SourPunchAmbi and look at her paintings.