*Puts on his 'Arting Basics' CD*
Actually, I've never given CGing tips but basically, I'll just go over stuff I've told newbies many times.
Traditional Medium
Traditional-anything is the best introduction on how to do specifics. Personally, I learned most of my form and proportions via drawing traditionally. I don't draw traditionally anymore because I can skip it due to my Cintiq, but anyways. What most fanime (anime fan artists) really don't understand is that you should ideally learn anatomy before even attempting to jump over to do Manga/Anime/Cartoons otherwise you'll surely have trouble later on. What I mean is, to break the rule you must first learn it; looking human but being stylistic. People bash Manga/Jap-anime for it's simplistic style but truthfully, industry-level artists know their anatomy and I'd really love to see some of those 'traditionalists' attempt stylistic (cartoons) artwork. Painting Digitally and Cellshading come from SIMPLE traditional principles but there are digital artists out there who've never drawn traditionally nor can they (apparently).
Lighting!
You have your shadows, midtones and highlights. Midtones should be defined
first, shadows
second and highlights
last. What you'll want to do is before placing down any colour, figure out your lighting. Use arrows like below or just make a quick mockup layer and paint the 'three' (mid, shadow and highlight). I used to not make a light study at all and jumped straight into it. You'll find yourself trying to figure out how something is lit when you could've easily spent that time 'prepping' it.
Here's two examples.
The ballllllllll! I whipped this up quickly in photoshop, but you can clearly see it's form because of the lighting. The shadow could use some work now that I look at it but again you can see that it's a round Three-Dimensional object.
This is one of my current WIPs. Purple arrows are the main light source, blue arrows are from the lightsaber and red arrows are 'bounced' light. The main light source is probably a lit doorway with this guy standing in a dim room. But anywho, you can clearly see based on that simple art principle of the balllllll, the character has form.
Quick tips
-Wireframes
When lighting something and you don't understand how an object 'works', create a
wireframe. Now I don't do this, but I've done it before for something complex and mind boggling.
-Black and White Study
Like the above example I posted, the character is in fact painted in black and white. This is known as a 'black and white colour study'. Apparently (I didn't do any art classes beyond high school) this is the most basic basic colour theory. You paint it how a colour should 'appear' in greyscale. The point then is you can simply make either a multiply or colour layer blending mode (look beside Opacity in Photoshop) and paint your desired colours over the top. You wouldn't go for a single colour, you'd need to add your skybox in the shadows (blue), etc.
-Reference
I always nag people to look at references. I usually do it if I don't understand something.
http://www.google.com/ is your best friend.
-Cellshading
Best way to cellshade is several layers. You have your background (choose something that is in harmony with your colour scheme, not black, white or florescent colours unless that's what you're aiming for), colour solids (skin, hair, clothing, etc), shadow and highlights and possibly 'effects'. You'll want to make good use of Blending Modes and Opacity for Shadows and Highlights.
Amazing Cellshading Tutorial.
-Recession
This is more about Photoshop lighting than 'shading'. When you've selected your colour solids (be it for painting or cellshading), you'll want to duplicate your colour solid layer and set it to multiply then paint (or marquee tool) on a new layer the 'mid tones' then the highlights on another layer, or so I've read/been told. I tend to paint my midtones over the darkened (shadow) midtone layer.
-Lock Transparent Pixels
Found below Blending Modes in the Layers panel. This is a godsend when you're doing lineart. What I mean is lineart should never be black unless it's intentional. You should go for a brown or colour that fits in with your picture's colour scheme. Or even go multiple colours, based on the 'midtone' (gold midtone would have a dark warm yellow line around it). Lock Transparent Pixels allows you to 'colour' the lineart or tamper with it without losing it's shape/form, i.e. only changes the lineart.
-Awesome Brushes
Brushes
-Hair
Hair is this funny thing that should never ever be straight, unless like I've said already, it's intentional. It should have (like computerwizoo7 said) beautiful dynamic curves which could be caused by the wind. You'll find a lot of artists draw hair dynamically instead of simply straight, flat and boring. Sadly there's some 'physics' involved in Hair and Clothing. If something doesn't look quite right, rework it!
-Perspective
For this one, I'll tell you to go read a book. :)
Critique:
The hair, like you implied, really needs a lot of work. It looks like you've drawn the end first and cut and paste'd it to make the hair longer while filling the lines inbetween. The lighting is flat. Why? Because she's lit from the viewer's eyes which shifts their (atleast my) attention negatively. She should either be lit from the left or the right (or top-left, top-right, etc). The large-bow looks off perspectively. It seems like it should be rotated around (in 3D space) to be a bit more 'symmetrically coherent' to the character. Her head, proportionally is too big (has too much depth) and the ear should be raised slightly to meet with the eyebrows height. I could go on about anatomy, but won't. Her forward leg (right leg) is smaller than the one in the
distance. The Human back/spine (female or male) won't do that kind of curvature like you've drawn, or atleast it looks off.
Messy unorganized post is messy. My brain now hurts. brb sleep. But yeah, these are just some basics that I go off. I could probably have a lot more to say. If you want some help with Photoshop, just
scream yell.