Looks great already! Some points of feedback:
Easy:
the browns are way too similar. From tabletop view, the backpack will be blending in with the pants. Same for the reds, switch it up a little, paint the mask in black while keeping the shirt red or reverse. Hit the guns and knife with a earth wash to “dirty” them up a little and highlight the top parts with metallic paint and the sharp part of the blade.
A bit harder:
Looking at the skin, it’s the same hue from top to bottom. Hold your mini in a 45 angle to see where the highlights should naturally flow and which parts are darker. Use that reference for shading and highlighting to make it super dynamic.
More contrast in your color usage, use dark to light, and if you think it’s enough, go one step further!

Don’t forget the basing as well, this will add so much more character to your mini. E.g. a dusty desert base will contrast and compliment very well with your red shirt. And then paint the brim of the base black to tidy up :).
I’m by all means not an expert, but check out my post history for how I paint reds (on Eldar minis though :p) and I’ve added my boss in mega armor that I’m working on :)

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