Pretty much what everyone has said about cloths but if you don't have "buisnessy cloths" that's ok. A few pointers for when picking them out.
1. Collared Shirt that doesn't show the boobies. Or if you don't have a suitable collared shirt pick a plain top and pair it with a button sweater/jacket/light coat.
2. Skirt or Pants must be below the knee. (or on the knee)
3. Minimal make up ( NO pink/blue eye shadows) GO for a natural look
4. Tie your hair back (if you know someone who can braid, that would look lovely)
5. Make sure the cloths are clean and if needed, ironed.
6. In-closed shoes (no sneakers/runners/what ever you call them lol)
7. Wear a bracelet that you can fiddle with to clam the nerves
8. Lots of antiperspirant (I put a giggle there but I am serious)
Best of Luck x0x0 I hope it all works out for you hun.