During my last trip to Rome (thanks, donors), I had business at the famous clerical shop Gammarelli.
I ask one of the helpful men at the shop to demonstrate how properly to fold a cassock. This is a useful skill. If you must pack or transport your a cassock, folding it properly can help to keep it from emerging wrinkled and creased.
I recorded this on an iPhone and the video wound up side-wise! Thanks to Fr. CD for converting it and making it useful. The business part of the video is a little narrow, but it is adequate.
Here you can see how to fold both a regular house cassock and a cassock with the shoulder cape or pellegrina (the example used belonged to a cardinal).
The video is in Italian, but the gestures and video are enough to let you know what to do. After this… practice makes perfect.