A very simple DIY I did a while ago. I got my hands on this top, that my brother didn't seem to wear anymore. It looked interesting itself, but it needed to get even better, so I did this.
I first cut the sleeves off a bit, then the collar line and the bottom of the top. Then I started cutting the fabric to about 1cm wide fringes. It takes a while, but it's not a big deal. When I finished cutting it, I pulled on each one to make them look more loose and natural and if you want to you can also shorten them up by lenght, because they can seem pretty long (just try it on while you're altering it).