This is just to show how i arrange my PSD file specifically for making textures.

^{This is how my Folder structure inside of photoshops layer manager looks when working on textures for 3d models. I keep an empty PSD file (one with no images in it) on my desktop at a resolution of 2048*2048 set up with this folder structure in the layer manager. This way i always have this layer structure set up whenever im going to start a texture. The reason i make the image 2048*2048 is because i can always lower the resolution if i need a smaller texture (keeping note that you should always work with at least a double sized texture to your final result.}

1. This is where the UVW map (exported from your 3d application) should go.
2. This is the "Alpha" or transparency maps should go. (*EDIT* this should be renamed to "OcclusionMap")
3. This is where the damage texture should go (Usually an overly on the diffuse map).
4. This is where the "specular" or shine map should go.
5. This is where the "diffuse" or color map should go.
6. This is where the "Normal map" should go.
7. This is just a temporary background color.

Examples of the textures involved