Get any blood off of it you can, especially those with white feathers. It discolors them if you let it set. Place the head under the folded wing and tuck it tight like a little pacjkage. Some recommend using a womans nylon stretched over it to help secure it, but I do not do that. I usually place a papertowel next to the bill or around it as no matter what, blood always seems to leak out and that helps absorb it from the feathers. Wrap it up tight and then plastic bag it. Get as much air out as possible. If you wrap it in a pillow case or something like that prior to plastic bagging it you can extend its life a bit in the freezer. Chest freezers seem to freezer burn less than the stand up ones.
Good luck.