For a number of years, I was an organizer, manager, and costumer for our local ZombieWalk/Fest and a haunted house. Here is one of my costumes, made by distressing a vintage garment and shoes, adding makeup, and a few practical effects. (My husband took the photos, as he was the official event photographer, so they are used with permission of the copyright holder. These were used for promotional materials.)
Distressing is a really simple way to add interest to a lot of kinds of costume pieces, although most useful in the horror/haunt type costumes. The most effective distressing isn’t just hack and slash. It helps to think about how and where your character would actually be moving in the costume, and working from there. And a great way to get some authenticity if you’re cutting with any kind of straight blade, or tearing on woven fabrics that tend to tear in straight lines, is to do some preliminary fraying and then put the whole thing through a wash and dry cycle. Acrylic paint in various colors and consistencies make good dirt and blood, of course, and are more or less permanent, which means you can wash the costume without having to reapply. And my fingernails are “nude” colored semi-translucent press-ons with purple and green nail polish applied to the underside. I hacked off the pretty tips and then scratched them on concrete to get then jagged and torn. With makeup on the hands after I applied the nails, they looked really convincing.