What you SHOULD wear:
- professional, moderately conservative clothing
- clothing that would be appropriate for a job interview in an office
- clean, pressed outfits
- business casual
What is business casual? Business casual is a comfortable, less formal version of classic business attire. Should men wear a suit? If you feel comfortable wearing a suit then by all means, feel free to wear one to the interview. If, however, you’re not accustomed to wearing a suit, don’t feel that you need to get this dressed up; a pair of pants and a nice shirt would be fine.
What about the naturalization ceremony? Taking the oath to become a United States citizen is an important event in your life. People will be bringing guests and some ceremonies may even have VIPs attending, so you’ll want to look your best. There will also be lots of pictures taken. USCIS addresses this issue in its Guide to Naturalization:
The naturalization ceremony is a solemn and meaningful event. Please dress in proper attire to respect the dignity of this event (please no jeans, shorts, or flip flops).
At the minimum, business casual would be appropriate but you could also dress up in a suit or dress if you’re so inclined. Leave the tux and ball gown in the closet or you’ll likely feel overdressed.