Need help with shading/drawing in general

[koori]

this is my opinion and that, so you dont need to stick to this, but anyway:
i think you should work more on the structure before jumping into color and shading, you know, a well structured drawing can look good even if the coloring and shadows are quite simple/basic; but a drawing with the most awesome color and that will still look confusing if it's not well structured

structure (Click to View)

by structure i mean you ability to see the shape you are drawing as a 3d form, understanding the shape and how all the sides of it are seen from different points of view is very important (but also tricky, this is not sth easy).

for example in this woody drawing:

the hair looks unbalanced, it seems like all the hair is on top of his left side of the head, and the slight backward bending woody's hair has is very difficult to see.
the nose looks also out of place, (maybe that's just your style, but looks weird to me)

this is how i would do it: (which is still not the best, look at those froggy eyes, omg)

*tip: i would suggest not drawing a straight line to show the hairline, some short lines in the direction of the hair looks more natural, just look at your own head, and touch it, caress it gently, feel it being a part of yourself and love it for what it is*

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drawing some little sketches from different point of view of the hairstyle you are going to is very helpful, it'll help you understand it and avoid wasting effort on sth you dont know at all how it looks.
but also, spiky hair like woody's is difficult in general, and more if you are just starting; i would suggest you to do henry's, jan's, jack's or monk's (it can help you making good looking head shapes before adding hair to it)

also in sai the bristle and fine-flat brushes are nice for hair

pf explained quite nicely shading so i'll skip that

color and stuff (Click to View)

take a look at this image, the hair color changes in light and shadow, but the value is not the only difference, saturantion and hue(more greenish or purplish blues) is important too. this also happens with the skin, clothes and pretty much everything.

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another interesting thing about color is the warm and cold hues thing.
instead of making red just red, a darker red and a lighter red think about the overall color temperature distribution and adapt your color to it.
one good way of doing this is to make light warm/cold and the shadows the opposite.

for example, the lit part of the headcloth on the left is orange; and the shadow part of the right one is brown and still they both look red(kinda). the same with the rest, doing this will help to avoid flat looking colors/shapes and also will give the entire drawing the feeling of being lit with the same light [source] which allways looks nice
*tip: is a good idea to change the color of the lineart to adapt to what's underneath or sorrounding it*

i hope this is helpful or sth