Right, I'm gonna try and explain what the issue is with PURTY PICTURES.
Here is what you are doing:
It looks to me like you're choosing your whole tonal range first (like my little palette up on the right), and then just doing a little bit of blending between the two.
I have a much simpler (and sexier) method that will get similar (but sexier) results.
HERE GOES.
1: DRAW YOUR THING. Choose two colours. One will be your lightest, and the other will be your darkest. Block in the rough shape of your shadows with a regular hard-edged brush.
2: Sample either of your colours, and paint over the edge of the other one with a semitransparent brush. (I usually use about 30% opacity, but anything between 30 and 60 is pretty good for this step)
3: Sample your new middle colour, and paint over the edges of your light and dark tones.
4: At this point I change the method slightly. I sample my second lightest tone, and paint over the lighter half of my midtones, plus the edge of the lightest tone.
Then I sample my second darkest tone, and paint over the darker half of my midtones
THEN I sample one of the middle tones, and paint over the... midtones of my midtones
5: This is the result you get from repeating step 4 for a little while.
6: LAST CHANGE: once I'm happy with the form from steps 4 and 5, I set my brush to about 10% opacity, and just start selectively repainting the bits that have the poorest transitions. Rather than painting thick bands over everything, I'm doing lots of quick little brush strokes over the roughest looking areas, resampling after each stroke, and trying to follow the form.
You don't necessarily need to go as far as I have with the repainting, or in fact, you could go further. It depends if you want more of a painterly look, or something smoother.
A shortcut that will save your life (if you're using Photosop, anyway): alt and click samples a colour, so you don't have to keep choosing the eyedropper.
Some bits to keep in mind: when you lay down your flats in step 1, it will almost certainly look as if the contrast is too great.
In fact, I might not have put enough contrast between my two colours.
If you find that you're not happy with the tonal range, just pick a new dark or light tone, and using a semitransparent brush, paint over the area that needs darkening or lightening, and then keep resampling and repainting until it's blended in as thoroughly as the previous colour. Banding, and then quick strokes.
Also, it might not be obvious, but I do all this on one layer per object. Usually if I'm painting something I'll have separate layers for different elements; say, the clothes and the hair and the skin will each have its own layer -- but the shading on the skin will just be part of the skin layer. Again, feel free to do whatever comes easiest. I would still suggest using a few different layers because it makes it easier to edit elements without disturbing other parts of the painting.
ALSO ALSO:
I can't believe I forgot this: when you're working on the rougher steps, use a bigger brush. As you start to get a softer transition between tones, start decreasing the size of your brush a bit to work in detail and "fine tune" what you're doing.
I try and limit the number of brush sizes I use, because it stops me from noodling away at little details, and it simulates traditional painting a little better, so it feels more organic for me.
(In exchange for my totally badass help there, you have to tell me how you got so badass at drawing the figure in perspective)
Here is what you are doing:
It looks to me like you're choosing your whole tonal range first (like my little palette up on the right), and then just doing a little bit of blending between the two.
I have a much simpler (and sexier) method that will get similar (but sexier) results.
HERE GOES.
1: DRAW YOUR THING. Choose two colours. One will be your lightest, and the other will be your darkest. Block in the rough shape of your shadows with a regular hard-edged brush.
2: Sample either of your colours, and paint over the edge of the other one with a semitransparent brush. (I usually use about 30% opacity, but anything between 30 and 60 is pretty good for this step)
3: Sample your new middle colour, and paint over the edges of your light and dark tones.
4: At this point I change the method slightly. I sample my second lightest tone, and paint over the lighter half of my midtones, plus the edge of the lightest tone.
Then I sample my second darkest tone, and paint over the darker half of my midtones
THEN I sample one of the middle tones, and paint over the... midtones of my midtones
5: This is the result you get from repeating step 4 for a little while.
6: LAST CHANGE: once I'm happy with the form from steps 4 and 5, I set my brush to about 10% opacity, and just start selectively repainting the bits that have the poorest transitions. Rather than painting thick bands over everything, I'm doing lots of quick little brush strokes over the roughest looking areas, resampling after each stroke, and trying to follow the form.
You don't necessarily need to go as far as I have with the repainting, or in fact, you could go further. It depends if you want more of a painterly look, or something smoother.
A shortcut that will save your life (if you're using Photosop, anyway): alt and click samples a colour, so you don't have to keep choosing the eyedropper.
Some bits to keep in mind: when you lay down your flats in step 1, it will almost certainly look as if the contrast is too great.
In fact, I might not have put enough contrast between my two colours.
If you find that you're not happy with the tonal range, just pick a new dark or light tone, and using a semitransparent brush, paint over the area that needs darkening or lightening, and then keep resampling and repainting until it's blended in as thoroughly as the previous colour. Banding, and then quick strokes.
Also, it might not be obvious, but I do all this on one layer per object. Usually if I'm painting something I'll have separate layers for different elements; say, the clothes and the hair and the skin will each have its own layer -- but the shading on the skin will just be part of the skin layer. Again, feel free to do whatever comes easiest. I would still suggest using a few different layers because it makes it easier to edit elements without disturbing other parts of the painting.
ALSO ALSO:
I can't believe I forgot this: when you're working on the rougher steps, use a bigger brush. As you start to get a softer transition between tones, start decreasing the size of your brush a bit to work in detail and "fine tune" what you're doing.
I try and limit the number of brush sizes I use, because it stops me from noodling away at little details, and it simulates traditional painting a little better, so it feels more organic for me.
(In exchange for my totally badass help there, you have to tell me how you got so badass at drawing the figure in perspective)