If you want more realistic, reflective metal, you need to establish what the environment around the knight is, since metal acts like a dull mirror of sorts. Of course, depending on the metal, you will have more or less detail in the reflected image (polished metal has a more detailed image, dull metal just reflects shapes and color). Once you know what colors/shapes are in your reflections, then you need to figure out how to conform those shapes to the shape of your armor. At the moment, your image is very cartoony, so I am assuming you aren't going to make this too realistic.
I've done a very quick overpainting to show you what I am talking about. I cleaned up some of the lighting and then added another lightsource (a torch behind the knight) and a blueish floor. The right leg (knight's left leg) is the only place I worked out any finalized detail. I worked blue into the under sides of the metal since the floor colors would be present in any surface facing it. I also added a rim light of orange to the rear surfaces that would be facing the torch. This is just one approach and my sketch is pretty unrefined, so I hope you can learn something from it. And there are also a bagillion ways to do metal, so please don't think that my approach is the only way.
Nice start so far.