When to use On/In/At?

There're a lot of different phrases where we have to use on, in, at.

Quite often it's difficult to predict the use of these prepositions there.

The most general rule (but not absolute) is:

Define the location of the object.

If it is on some surface, use 'ON' (ON the wall/ floor/ table/ ceiling/ platform/ etc.).

If it is in some volume (space), use 'IN' (IN the office/ room/ box/ corner/ sun/ rain/ etc.).

If it is neither in nor on smth, use 'AT' (AT home/ work/ the airport/ the hotel/ etc.).

This general rule helps rather often.

For example, we can differentiate:

ON Cuba (as an island) and IN Cuba (as a country)

IN the corner (as space) and AT the corner (as a meeting place)

IN the (high) grass and ON the (cut) grass

IN the book (inside it, between pages) and ON the book (its cover)