Preheat the oven to 250° F.
Remove the ham from its packaging, and place it face down in the roasting pan.
If your package has any juices in it, pour them into the bottom of the pan, along with about 1 cup of water; this will help your ham to stay more moist.
Cover the ham tightly with foil (all of it but the bottom, so the juices can run out into the pan).
Bake the ham according to the instructions in your packaging; usually, it will require you to bake it for 12 to 15 minutes per pound. So a 10-pound ham will bake for about 120+ minutes.
About 45 minutes before the end of your bake time, empty the glaze packet into a small saucepan, along with 2 tablespoons water.
Bring the glaze to a boil over high heat while stirring constantly.
Remove the glaze from the heat. About 1/2 hour before end of cook time, remove the ham from the oven, take off the foil, and apply the glaze all over the outside of the ham with a basting brush.
Finish baking the ham, glazed and uncovered, for another 30 minutes or so.
When the ham is done, you can bring it out of the oven, let it cool just a bit, and slice it for serving.