You get your new uniforms and they look all nice and pretty. Unless your characters are in boot camp chances are their gear should be beat up! This is something that no one will notice UNLESS you don't do it.
First Step for Aging Uniforms
Wash them, and wash them some more and when you done with that wash them again. I used hot water to fade the colors and to break down the fabric.
Second Step- Beat Them Up
We used metal brushes and a paint stripper that plugs into a drill (hardware store in the paint department). The paint stripper pad will shred fabric in a heart beat, in fact wear some gloves just in case. You could also tie them up to the back of your car and drive down a dirt road...?
Third Step- Add Some Age
This fabric dye is EVIL- DO NOT USE NEAR CARPET or clothes you like and wear long gloves. Evil but awesome stuff. They sell this brand of dye in lots of colors at fabric and craft stores. I used it to edge the seems of the clothing.
If you need to age leather goto Tandy Leather and if you have other equipment try painting it (see Metalize Weapons tutorial).