So, I decided to make this for you guys, though I'm not a very good teacher. I in no way think I'm all that good at shading, but maybe you can use it to help ya out to get better then move on.
I used my character Echo for this. I was going to use a baby picture I was going to work on, but I decided to keep this neutral.
This tutorial works for Paint tool sai. It's possible it might work on others, but I haven't tried.
Full size: [link]