Prepositions are one of the toughest areas of English for non-native speakers to learn correctly. (In my experience, mistakes involving prepositions are among the most common from Indian learners who have learnt to use articles :-))
The Language Log wonders today about prepositions, starting with In or on? Experience the power of splash screens by Mark Liberman, At that second, on that day, in that year by Geoffrey Pullum, an anecdote Preposition day at Language Log by Roger Shuy, a more detailed look In the car, on the bus by Geoffrey Pullum, and finally an attempt at a “logical” explanation, Dimensions, metaphors, and prepositions by John Lawler.
English is hard :)