At in on

AT se usa con las horas (at 10:00 am), momentos del día (at night) y con nombres de festividades (at Christmas, at Easter).
IN se refiere a partes o divisiones del día (in the evening), meses (inNovember), estaciones del año (in winter) y años (in 2004). IN se usa también para señalar un período en el cual algo tendrá lugar (in nine months' time).
ON se usa para los días de la semana (onMonday), para partes o divisiones del día (mencionando el día de la semana) (on Monday mornings) y para las fechas (on 15th May, on November 5th).
Tips (Consejos)

IN - ciudades, pueblos y paisesejemplo: I live in Madrid, in Spain.

AT - lugares concretos ejemplo: The train arrived at the station. The children are at school.

Estar en el trabajo = to be AT work
Trabajar en un banco = work IN abank

IN the corner (esquina) si estas dentro de una habitación
AT ó ON the corner si estas en la calle

AT the front ó AT the back para hablar de posiciónes dentro de un edificio
ejemplo - Ialways sit at the front of the class.

ON si te refieres a algo que esta escrito en una pagina ó una hoja

IN a book, IN a newspaper, IN a magazine si no te refieres a la pagina
ejemplo - I saw aninteresting article IN yesterday´s newspaper.
1 How many people can you see ...... the photograph?
2The most important news is always ...... the front page of the newspaper.
3 Please use the mainentrance ...... the front of the building.
4 The phone number wasn´t listed ...... phone book.
5 When we arrived ...... her house she was very surprised to see us.
6 The supermarket is ...... thecorner of the high street.
7 I like to sit ...... the back of the cinema to get a better view of the screen.
8 I live ...... a big city.
9 He works ...... an office
10 Madrid is ...... Spain.

1| one | 1st | first |   |
2 | two | 2nd | second |
3 | three | 3rd | third |
4 | four | 4th | fourth |
5 | five | 5th | fifth |
6 | six | 6th | sixth |
7 | seven | 7th | seventh |
8 |...