In

• a place with three dimensions

On

• a surface
• a line

At

• a point

Other

• At work
• At home
• Often use at with places where people study

             e.g. at school, at university

• Often use in or at with buildings
• Use in when we think of the building itself
• In + city/town
• In + street
• At + house number
• On + floor 

Source:

F.1 W.S