The most professional business outfit is a plain coloured suit made with good material such as wool or a woollen blend, with a knee length skirt (just below or above the knee) is the most professional. The best colours are black, navy, dark blue, or grey. If you wear a dress make sure it is worn with a jacket and adhere to the above guidelines to keep it professional and business like. Some women prefer to wear a trouser-suit; if this is the case the trousers should rest at the top of the foot or shoe without creasing when your leg is straight.
Blouses and tops worn under your jacket should blend well and complement the suit. Choose natural materials such as cotton or silk. Be very careful with patterns, one pattern is probably sufficient for formal business attire. Be careful that the neckline is not too low. Avoid sleeveless tops unless you intend to keep your jacket on.