The short version is in this post; a more detailed explanation which includes some exercises to practice can be downloaded here (prepositions-at-in-on.pdf). The answers to the exercises are available here.

Prepositions of place

In general we use:

  • at a POINT
  • in an ENCLOSED SPACE
  • on a SURFACE

Examples:

  • Peter is waiting for you at the cinema
  • Do you live in Italy?
  • Someone has spilt wine on this menu

Prepositions of time

In general we use:

  • at a PRECISE TIME
  • in a PERIOD OF TIME
  • on a DATE or DAY

Examples:

  • We usually eat lunch at 1 p.m.
  • Are you going on holiday in June?
  • Where will you be on your birthday?