Hi John, a great looking figure and has been said it could do with some variation between the highlights and the lowlights, are you using oils or acrylics because they have different methods of toning. With a figure of this scale there is an enormous amount of detail that you can get in.
If your using acrylics you need to set out your paints mixed and ready to go, and you need about 6 colours for the uniform
1 base colour
2 base colour plus small amount of whit
3 base colour plus a larger amount of white
these are for the highlights
4 base colour mixed with a little burnt umber
5 base colour mixed with more burnt umber
6 burnt umber
You have to imagine that light is coming from directly over your figure, so that on creases lighter shades are on top and darker are underneath. you can get a good idea of where you need to shade by shining a lamp directly over the figure.
Paint your base coat and then start with the shadows so underneath each crease add your first darker shade leaving a small amount of your base coat showing and then the same again for the darkest shade
Then go on top of the creases and repeat the process with the lighter shades, You will probably find that you can see a distinct line between the shades so the next step is to mix 6 more colours and they are intermediate colours so mix a bit of 1 with 2, 2 with 3 and so on and with these colours just wash them over the lines between the previous shades and you will find that they blend the colours together.
there is also dry brushing, for instance if you look at the hair it looks like you have used black which is a very harsh colour, a better colour for dark hair is burnt umber mixed with a little black, then when its dry add a bit of white to the base colour, and using a flat brush, wipe as much paint as you can from the brush onto a tissue, and then brush it over the area of the hair, it should then just highlight the raised areas, this technique can be used for anything, but try not to use straight black its very harsh.
For his document case, and a good colour for leather is burnt umber mixed with a little raw umber, just add a bit of orange for the highlights and do the shading in blue, you will find that the orange gives it a worn look and blue is much better for shading burnt umber than black.
There is also a little tip for making things like the edges if collars and where two bits of material overlap and that is to wash it with a burnt umber wash, used very thinly and lightly apply it to those edges, it really makes them stand out.
I think you have a very sound base to paint a great figure there and your work is very neat it just needs to be made to look not so new. as you say this is a practice figure so practice
heres a picture of the colour sgt that i finished a short time ago, as you can see on the jacket i base coated it with red and then darkened the lower part of the creases with mixtures of red and burnt umber in some places going down to straight burnt umber and for the highlights i used red and added orange sometimes going up to yellow.
Dont be afraid to experiment, if it looks wrong just paint over it, but be creative and look at actual things like leather belts and boots for ideas. or look at how your cloths look under certain lights, its all there in front of you.
Hope i havnt waffled on to long and i look forward to seeing what you come up with
Paul