Do not dress any bird you intend to take to a taxidermist. Immediately after retrieving your game bird, wipe any blood off its feathers using a clean cloth. Dab the cloth lightly in water if necessary to remove stubborn stains. Do not rough up the feathers; instead, wipe in the direction they lie. Stuff cotton batting in the bird's mouth and nostrils if you can, to prevent further blood leakage.
If your car is nearby, lay the bird on clean paper in a place where it will not be disturbed. Be sure to smooth out the feathers before laying it down. If your transportation isn't accessible at the moment, you can roll your bird into a cone of newspapers or a paper bag and carry it with its head down. (If you don't carry it head-down, blood could drain through the nostrils and beak and stain the feathers.) Don't wrap your trophy bird in a plastic bag when taking it home, as this will cause the bird to retain its body heat and spoil.
Once you're home, double-check to ensure your bird's feathers are all lying correctly and smoothly. Wrap it in paper or a plastic bag (it's fine to use a plastic bag at this point), and freeze it solidly. Keep it frozen for delivery to your taxidermist, as chances are he or she will likely have to store it for several weeks before mounting it.