Hello! These are really good! I love the colour scheme on the first one and how you rendered her top part of the dress!
But I do have a few ideas of how you could improve it.
The 1st one is your piece just inverted to black and white to see the values better.
and the second one has a bit of a paintover .
Overall the values of your artwork are good but there were few spots where you could push it further.
The basic concept for making things pop out a bit more especially if it is a concept art is to draw light things on the dark background and dark things on the light background.
Now back to the paintover version I did to help you understand what I mean by all of it 
For example:
I've brightned the bottom part of this picture to make the dress pop a bit more coz before they were almost the same value and it looked flat.
I also pushed value brigther around her waist area as it gave an illusion that there is no distance between her and the background at all.
Then I tried to define the light sources which was very tricky but since her face is so well lit I added more light to the metallic part of her dress to make it appear rounder and to the bottom part of the dress.
and then I also made her head slightly smaller because her hands are pretty small compared to the head size.
I hope this helps and your artwork is really cool, I think this Mace lady design is unique and you definetly should post your art online and get yourself out there
P.S.
For panting clothing you need to look for references and see why this fold appears here and there, is the fabric thick or thin and just practice it.
How to paint folds
How to paint metal Part 1 by Swatches - this one has 3 parts and I do recommed trying out these techniques and see for yourself how it works.
and about Bard picture I am no really good at foreshortening as i usually check ref for it.. but
Basically make sure your anatomy and pose is on point. Search for images of ppl playin this instrumens, see how their arms are located and where they rest their right arm.
my try here might not be correct 
so i would definetly recommend you to look at multiple references ;>
and again, hope it helps 
