Congrats! Mine have only been laying about a month so I'm still really excited when I go out to collect eggs every day! I think its great that you want to save it!
Carefully poke a small hole in the top, and one slightly larger in the bottom. Gently stick a toothpick/skewer inside to scramble the yolk a bit. Hold the egg over a bowl and place your lips over the smaller hole and blow out the contents. When the shell is empty, rinse several times with water and let dry completly.
From my Hobby Farms Home magazine, Durham's Rock Hard Water Putty can be used to help reinforce the eggshell. They say that it doesn't expand or contract while drying, so it won't damage the eggshell. They say to inject the putty in the eggshell with a needleless syringe, using enough to leave a thin coat on the entire interior surface when you shake it around (make sure to cever the holes with your fingers when you do this) and then let the extra drain out. It says it may take a couple of days to dry completely.
Then you can do whatever to the egg to decorate it if you want, I am going to attach a jewlery hanger, but otherwise leave it as is.
I think its great that you are going to make your first egg a Christmas ornament! My DH said he is going to blow out our first egg also and frame in in a shadow box and put it in the coop--- kinda like a "first dollar!"