Windows and doors, closed at all times!
Why?

Most wallpapers need to be acclimated to the site until they’re fully dry and settled.
This can take from 1 day to even a week.
When A/C is running and doors or windows are left opened, the temperature and humidity will vary considerably.
Certain materials will react to these changes, for example contract vinyls, they’ll shrink and expand upon these changes, when that happens they can peel off and dry unevenly.
Not all materials can be fixed after this occurs.
Also, when humidity and heat gets inside the site, the A/C will condensate and registers will drip, staining and damaging the material.