All main dining rooms have the same menu, but the specialty restaurants have their own. Since this is your first cruise, keep in mind that you can order more than one, or as I prefer, order the lobster and the steak entree and make it surf and turf.
Many times my wife and I each saw an entree we wanted, and asked for a third to share. Ask for both soup and salad if you want, or two desserts. Don't fall into the mindset that you have to order one item from each course. Every waiter I've ever had cruising was glad to cater to what we wanted, and I was never made to feel piggish. On our last cruise we were seated with a younger first timer couple and everything we asked for extra they brought to them as well and they got a big kick out of it. It was a fun table.