Abrasives

Faux garment leather is not as durable as real leather. You will generally want to be more careful and use finer abrasives.

Try a finer grit sandpaper, around 150 – 200 grit, or a fine steel wool.

Paint

To recreate the look of worn leather, a light brown paint may be your best option to mimic the wearing down of the surface of the garment.