Maybe it can help :)
IN --> Something GENERAL/BIGGER
TIME (centuries, decades, years, months, weeks)
LOCATION (country, city, neighborhood)
Source of information (written material: book, magazine, newspaper, etc.)
Ex.: I live in Rome.
Let's meet in July.
I read it in a book.
ON --> Something MORE SPECIFIC/SMALLER
TIME (days, weekend)
LOCATION (street, avenue)
Source of information ((electronically: the radio, the internet, tv, etc.)
Ex.: I live on Main Street.
The garbage truck comes on Wednesdays.
Let's meet on Friday.
I watched it on TV.
AT --> Something VERY SPECIFIC/SMALLEST
LOCATION (address, specific location)
Ex.: I live at 33 Main Street.
Let's meet at 10 o'clock.
I am posting this IN July ON Friday AT 10:00 a.m.