BY:
Were you sitting BY (beside) the door?
Joe parked his car BY (beside) mine.
The police station is BY the court house, isn't it?
ON:
The pencil is ON the desk.
He sat ON the fence.
Mary is not thinking well ON that occasion.
AT:
I live AT 979 A. Agoncillo St. Indang, Cavite. (JUST an example.)
Meet me AT 7-ELEVEN today.
I shall see him AT the mall.
IN:
He lives IN the country.
I'll be there IN an hour.
The child ran down the steps IN tears.