If your cruise isn't until 2026, you might not be able to reserve yet. Those reservations usually open up about 14 months before, but you could start checking.
You can use the app or bring up the Celebrity website on your device. I like to use my laptop as it's so easy to see everything. Sign in and click on Plan My Cruise and then click on dining. You will then be able to see if you can make reservations yet.
If you are on an E class ship, you will have 4 dining rooms to choose from. You can choose to eat in one, where you can order from all 4 menus, or you can pick and choose to go to different restaurants.
There is a pro, to choose the same restaurant in that you will likely get the same wait staff every night and they learn what you like really quickly. An example is that the first night I ordered an ice tea and thereafter, ice tea came out to me almost as soon as I sat down.
We get bored and like to feel like we're going to different restaurants so we choose to mix it up. Personal preference.