Spanish-speaking students often confuse these two prepositions as both mean “en” in Spanish. These are their differences in English:

IN

Inside an enclosed place (building, office, room, bag, box, etc.) or a territory with borders (region, province, country, city, garden, etc.). Expressions with in:

in a room

in a building

in a garden

in Italy/Spain/France

in Venice/Madrid/Buenos Aires

in a village/town/city

in a pool/river/sea

in a row/line/queue/street

in a photograph/picture/a mirror

in the sky

in the world

in a newspaper/book/magazine/letter

AT

Shows a point in space where something is happening. It´s a point in a map/territory.

at the bus stop

at the door

at the window

at the traffic lights

at the church

at the top/bottom

at reception

at the beginning/end (of a street, book, film, etc.)

ON

On is used with surfaces (“sobre” in Spanish) and lines:

on a street/avenue

on the beach

on the river

on a sofa

on a table

on the floor

on the ceiling

on a shirt/skirt/jumper

on page 7

Expressions where we can use more than one preposition:

1) I live in Kingston Street. The bar is on Queen Avenue.

2) I went to a concert at the Royal Theatre. The chairs in this theatre are all blue.

3) Let´s meet at the cinema. It was quite cold in the cinema

4) The train doesn´t stop at Benicassim.. She lives in Benicassim.

5) I was still in bed at 6 a.m. I got up at 8 today.. I like reading on my bed. 

6) Lucy is in hospital. I was at the hospital for a routine check-up this morning.

7) Jack was sitting in the back/front of the car. The garden is at the back/front of the house.

8) There´s a plant in the corner of the room. There´s a pub at/on the corner of the street.

9) I like the label on the this bag. What´s in that bag?

10) There´s someone at the door. Look at the notice on the door.

11) I found the ad in yesterday´s newspaper. The exercise is on page 10.

Here is an exercise to practise.