I learned a nice little illustration when I taught ESL. Draw a triangle and divide it into top, middle and bottom. Put "at" in the top, "on" in the middle, and "in" in the bottom. This triangle works for location and for time.
The top is the smallest, so it is the most specific:
I live at 156 Escalon Street
I am staying at the Grayson Hotel.
I will meet you at 3:00
The middle is next, and is a more general/broader location or time.
I live on Escalon Street
I will see him on Monday.
The bottom is the largest, so it goes with the larger space or period of time.
I live in Ohio.
My birthday is in July.
He was born in 1967.
This triangle doesn �t work for every location or time situation, but it is nice for teaching general rules.
Bruce