Creating a texture in GIMP with a grid

I am not really a gimp user, so I hope this is helpfull. I know the final textuer is not as good as I normaly do. But normaly I use Blender and photoshop to make textuer maps.

The best adivce I can realy give is to just play around and learn what all your graphiccs editor can do. Oh, and if you know what you want to make, try and have a lot of references on had.