The Direction of Laying Wood Flooring

QUESTION
I have a client who wants to install hardwood flooring and was asking my advice on the correct direction. Is there a rule of thumb regarding which direction to lay the planks? One rule I’ve heard is that it should be laid the opposite direction of the traffic pattern. But that may be different in different rooms.

ANSWER
Direction Matters According to One Flooring Installer - The normal method for installing hardwood strip flooring is to lay the boards perpendicular to the floor joists. The boards can be installed parallel to the joists, but an extra layer of sub-floor plywood must be added.