Typically a good misting with water daily will help keep the greens nice and fresh.
Outdoors – you will want to keep an eye out for heavy snowfall that may weigh down your greens and distort the branches. Gently use your hands and shake off any excess snow to keep your greens nice and shapely. Yellowing/browning will slowly occur and start off with the greens that are less tolerant of the deep frost (i.e. cedar, pine, etc.). Remove by pulling out or clipping those cuttings to keep your arrangements looking nice.
Using milk to spray the greens to add a nice shine.