Adding Dirt

Hey All ,
Just a quick post , i'm kind of stuck trying to get my repaints look 3D , they look at the moment 2D because of no dirt! I was wondering if anyone was willing to teach me OR if there is a tutorial on adding dirt to an aircraft to make it more real. thanks.
Just a quick post , i'm kind of stuck trying to get my repaints look 3D , they look at the moment 2D because of no dirt! I was wondering if anyone was willing to teach me OR if there is a tutorial on adding dirt to an aircraft to make it more real. thanks.