Use *in* for : - months/years/long periods of time - countries, cities, areas - buildings ("he is *in* the office", not "he is *on* the office") - times of the day ("in the morning") Use *on* for : - days, and specific dates ("Christmas is on the 25th of December") - specific streets etc ("My house is on Queen Street") - public transport ("He is on the bus") - directions ("It is on the right beside the station")