The ideal of chivalry which is essential to the modern concept of the knight as an elite warrior sworn to uphold the values of faith, loyalty, courage, and honour is usually used to outline a knights code of conduct in all things he does. They were also expected to help those of lesser or weaker stature as a part of their everyday lives.
When dealing with princesses and noble women the rules for them would be the same as the rules for everyone else I would think. Don't talk to them in private, only in groups (of the women not in groups of men), don't address them unless you are first addressed and even then for longer conversations that were not of an implicit nature (secret rendevous) it was sometimes appropriate to obtain the father or husbands permission.
Simple stuff like that it also depends on the circumstances in which the knight in question is dealing with the women. If he runs upon them in the forest in need of immediate saving from bandits he would take more liberties with them than if he came upon them with a broken carriage wheel.
Try reading Arthurian legends as they deal a lot with the way knights dealt with people of every class.
Hope it helps. D.
