I would skip Macy's. It is a waste of time, the place is a zoo, hot and stuffy, and a 10 deep line for the men's bathroom. If you want to see store decorations, just walk down 5th Ave and look at the window decorations, and it is on the way to Rock Center where you can see the Christmas tree and ice rink. Careful, during Christmas I have seen many people eat it looking around instead of watching their step. Cold hard cement = ouch!
If shopping, head to SOHO. If you get hungry, grab a chicken rice from a halal cart or a dirty water dog.
My trips to NYC tend to be food and shopping related because I have done the touristy stuff far too many times. I would however recommend hitting MOMA.
Maybe a stop in Little Italy. This is very touristy, and since you have never been, you may want to have one of those cliched red checker table cloth dinners at one of the restaurants. I find all of them pretty ordinary, food wise.
My must eats (especially for first timers):
1. Peter Lugers (cash only) - get the porterhouse for two, slab o bacon, German fried potatoes and dessert w/ schlaag.
2. Pastrami Queen - pastrami on rye
3. Domonique Ansel - DKA
4. Prince St Pizza - Spicy Spring
5. Katz - pastrami rueben or brisket sandwich, also hot dogs are great too
6. Carnegie Deli - just for kicks, you can just walk by and look at how enormous the portions of food are.
7. Dough - for excellent doughnuts
8. Minetta Tavern - Black Label Burger, pricey yes, but easily the best burger I have ever eaten in my life.
Enjoy, if you need more food rec's, LMK. Oh, and one more thing, get familiar with the subway map if that is your primary mode of transportation.