Well, since a lot of newbies very often paint their metal by dodge and burn like they do on other materials, I decided to make a little tutorial on how metal
really reflects light.
Metal reflects lights in different ways, depending on the shape of the metal type. Here's the basics:
Spheres:

The shadows and the highlights really follows the shape of the sphere (as you can see). If there's normal sunlight, the sun will create a pure white spot as seen in the image. Spheres can be compared with round, convex shaped shields, some pauldrons (you see if it is kinda shaped like a sphere or not), and even some breastplates (mostly those from the 16th century).
Cylinders:

(the image is showing how it would look on the unwrap)
The white spot in the sphere is replaced by a white line, that almost always follows the direction of the cylinder. Often there's alot of contrasts on cylinders too, so don't hesitate to shade very dark after a really bright highlight. The effect is kinda the same on cones. Objects that can be compared with cylinders is arms and legs, some breastplates (as on spheres, depending on the shape), and even helmets. They are often some kind of mix between cylinders and spheres, so uhm.. shade somewhere in between. :)
Overlapping and edges:

(the image is showing how it would look on the unwrap)
At the edges of the metal part, theres (almost) always a line with highlight. In this example, I've made a quick skin on some kind of upper thigh protection (cylindrical of course). As you can see, even on the darker lines, theres highlighting on the edges. This will really make your different parts stand out so you clearly can see if it is above, under or beside.
I hope this help someone, and good luck!
And remember, these example images are just crappy 2 second jobs, you can get the effect alot better with more time