Simply put, don't ski up the piste.  
​Guidelines from Mountaineering Scotland: 
https://www.mountaineering.scot/activities/snowsports-touring/code
See summary form (a nice poster you can put up on the wall!):

https://www.mountaineering.scot/assets/contentfiles/media-upload/Ski_touring_and_ski_resort_areas_code_web.pd