Step 1: Choose a type of armor. (If you're using this skin for PVP, use diamond or chainmail!)
Step 2: Draw an exact copy of the armor on the jacket and hat layer.

Tip 1: You can put any skin under the armor. But remember that you shouldn't put hat layers on the skin under.
Tip 2: Try finding out the color codes of the colors on the armor and then use a skin creator that allows you to use color codes.
Tip 3: Put the armor on the legs on the base layer and put the boots on the jacket layer.

Step 1: Put a 2x1 white rectangle where the mouth would be on the base layer.
Step 2: On the jacket layer, put a skin colored 2x1 rectangle on the exact same spot as the white rectangle that was put on the hat layer.

Tip 1: Try putting the mouth 1 pixel above the bottom of the front head base.

Step 1: On the base layer, put mechanical parts that will later be covered by the armor.
Step 2: Add various armor pieces on the skin.

Tip 1: Try leaving open spaces at joints so you could see the some of the mechanical parts.

Step 1: On the base layer, draw the vest without pockets.
Step 2: Add the pockets.
Step 3: Add any other appropriate details.

Tip 1: If you are putting pockets together, make one of them darker to show that they are different pockets rather than one.
Tip 2: Try adding medpacks, ammo bags, etc.