(Paris map via Plan de Paris)
Consider the Seine to be your Fifth Avenue. All addresses leading away from the Seine increase in number. (So, right bank: increase northward, left bank: increase southward). Also, addresses running from east/west increase with the flow of the Seine (westward). So if you ever get disoriented or are unsure which direction you're walking when you come out of the Métro, take note of the surrounding addresses and it will (hopefully) help you feel a bit more centered in the City of Lights.