For me the day of was smooth. Actually arrived a bit late but got signed in and told to wait. My name was called after 10 minutes. Questions were mostly how we met, if we live with anyone or just us, how our families get along, what my spouses birthday was lol, I think that was basically it besides confirming information on the application. I bought extra docs but they didn't need them just out passports, drivers licenses, and green card. I only used the civics test app to study and I was good.