I can does shading!

Please ignore the stars. I don't like using them. <img src="e.deviantart.net/emoticons/let…" width="15" height="15" alt="" title=" (Lick)"/>

Since you're focusing on shading and tones, I will also focus on that. <img src="e.deviantart.net/emoticons/b/b…" width="15" height="15" alt="" title=" (Big Grin)"/>

You do seem to know about light sources and what they do, but try to be more creative with your lighting! Try putting the light source in different places, like above or on the side.

And make sure your lighting is logical! There's a highlight on the bottom of the head but there's also a highlight on the top of the hair! Unless there are two light sources, that would be very unlikely to happen! Though hair and eye shines are awesome and cool-looking (and yes, they are), make them make sense! If the light source is from the top, then highlights are bound to be near the top of objects. It'll help your pieces look more realistic and your characters more 3-dimensional.

Highlights also tend to vary in value and softness. Some edges of light tones are soft, some are hard. This is even more evident in shadows. Take a ball or cylinder near you, put it on your desk, and turn off your lights, but light your object with a lamp or flashlight. Notice how the edges or shadows vary. The shadow cast by your object should have a harder edge than the shadow on the object itself! I'm not going to explain why because that would take A Really Long Time, so here's a tutorial: [link]
(Check out her other tutorials, too-- they're awesome.)

Now to apply that to your drawing. The hair would cast a hard-edged shadow on the face, while shadows on the head cast by it turning around would be softer. However, fur does strange things to shadows and highlights. It's a bit complicated and I'm not good at it myself, so I'll just tell you to add texture.

Another thing I might add is that shadows have different colors on different objects. Instead of just adding black or grey to shade, try using a darker blue on the hair, or an indigo for the purple fur. Go nuts!

I'll also critique things other than shading.

Firstly, your line weight is always the same! Don't be afraid to use different thicknesses for your lines! Thicker lines are usually used where an object is darker or closer, or where you want the viewer to focus their attention to. Line can be a very useful tool! Try looking at comics to see where artists thicken their lines or make their lines thinner. Fight scenes in manga are where I think it's most evident. <img src="e.deviantart.net/emoticons/let…" width="15" height="15" alt="" title=" (Lick)"/>

About the hair, remember that it's made of separate strands, not just one big clump of hair (that would be heavy)! Try breaking down the hair into separate chunks that, when put together, make more realistic hair!

Also, try using more swooshy, loose lines. It'll help you draw more freely and make your drawing less stiff! This is especially important with hair, which is already swooshy!

In this view, the hair is reeeaaalllyyy focused on, mostly because of the color and brightness. Unless this was your intention, try to find an angle where the areas you feel are important look important. Something that I do when I think I'm almost done is close Photoshop, go do something else for a while, then come back to my drawing with fresh eyes. That way, I can see what people see first when they look at my work. Most of the time, I see EVERY MISTAKE EVER IN ETERNITY. But it's easier to fix mistakes if you know where they are! When you look at your drawings, note what strikes you first! Is that your intention, the message you want to convey?

There are A LOT of tutorials here to help you! Go explore the tutorials section! That's what helped me make a huge leap in improvement, and I have no doubt it will help you too!

Thanks for reading my critique, sorry for rambling, and happy drawing! If you have any questions, just ask! <img src="e.deviantart.net/emoticons/l/l…" width="19" height="19" alt="" title="La la la la"/>