Continuing from basic colors blocked in...
At this point I would assume you have already blocked in the basic colors as described in the Digital 101: Basic Coloring tutorial. You may also wish to look at the Shading 101 tutorial as proper shading can really improve a picture! See the Photoshop Brushes tutorial for information on configuring your brushes.

Special thanks to ~Refleximage for use of his line art for some of the examples used below.

Step 1
Okay so, texturing to look like metal. I've got a basic blue color blocked in and begin by using a 8 to 12 pixel brush and shading in a patter of lines.

Step 2
Moving on to step 2 - lots more line shading with the same color (I press harder to make it darker 0 as always on med pressure).

Step 3
More of the same process using a darker color. Notice I'm creating the shape of the armor - leaving areas where the highlights will be.

Step 4
I go back in with a lighter color and a smaller brush and add more highlights.

Step 5
Now with an even lighter color I add the brighter highlights. When blending and adding highlights I press lightly and move in a circular motion.

Step 6
Now I use a darker and lighter color do add some scratches and dings.

Step 7
Now I colorize my line art (see the Basic Sketching/Line Art for how to do this). To a color that blends in with the metal colors.

Step 8
Now I blend the colorized line drawing in with the colored layer. To do this I merge the layers together, zoom in, and carefully smudge WITH the lines (not against them). I also use a small brush to make corrections/add some last highlights.

Finished
Okay! It's all finished. As you may have noticed in the close ups I work pretty large - so when you shrink the image down to the size it's "planned" to be viewed at it looks really good/detailed. You can also go in with the Dodge tool and add some softer glowing highlights as shown here. And that's it - done!