A fresh tree will have flexible needles, ones that give and spring back when moved by the hand. A tree that is dry will have brittle needles, ones that break off when rubbed or bent backwards. Avoid ones that are dull green or lack that fresh, just picked look. Bounce the tree on the ground a couple of times. Yellow and discolored needles shedding are normal.
Needle drop is common on all types of evergreens including pines, spruce and firs.
What you want to avoid is a lot of dull green needles dropping from the tree. This indicates that the tree has already begun to dry out. If it sheds needles outdoors it will drop them all over the carpet by the end of the season. Once the tree is selected transport the tree home carefully. An exposed tree strapped on top of the family minivan or SUV is not the proper method.