Enter a House right Foot fore most
(Petronius). It was thought unlucky to enter a house or to leave one's chamber left foot foremost. Augustus was very superstitious on this point. Pythagoras taught that it is necessary to put the shoe on the right foot first. “When stretching forth your feet to have your sandals put on, first extend your right foot” ( Protreptics of Iamblichus, symbol xii.). Iamblichus tells us this symbolised that man's first duty is reverence to the gods.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894