First, let me say that your work is quite good for the time you've been painting, but there's always another step that you can take.
From the pictures you posted, I'd recommend that your next steps should be:
Thin you paints a bit more (and perhaps use an extender). The chalky appearance of some of your highlighting and shading is usually caused by improperly thinned paint.
Push your highlights higher and shadows deeper, particularly on the faces of the figures.
Blackline the borders between colors to make for crisper color transitions. (Blacklining need not be done with "black", btw.)
And you might want to take a look at some miniatures photography tutorials (like the ones on the Reaper site). Good lighting and a simple backdrop will make your pictures look much better.
HTH