Think of business formal as your nicest work outfit dressed up. For men this means a dark suit in black or navy blue. A crisp, collared button-down shirt should be worn underneath. If anything, stay a bit more conservative than you normally would, and keep prints to a minimum. A printed tie is acceptable in a classic stripe or plaid -- no loud colors or patterns. Shoes should be leather oxfords. Ladies can opt either for a matching pant or skirt suit and a button-down shirt underneath as well. Stick to a classic closed-toe pump. No flats or sky-high stiletto heels.