Basic rules for using: in, on, at, & to

IN

Months: in May, in January
Seasons: in winter, in spring
Countries: in Greece, in Malta
City or town names: in New York, in Yokohama
Times of the day:　in the morning, in the afternoon, in the evening (but, we say at night)
Years: in 1978, in 2004
Decade: in the twenties, in the '90s
Future: in a few weeks, in a couple of days, in six hours
Note: We do not say "in this year." Instead, you can say "[do something] this year," "[do something] during this year," or "[do something] later this year."

ON

Days of week: on Friday, on Monday, on Sundays
Calendar days: on New Year's Day, on Christmas Day, on October 22nd, on April the 19th
Weekend(s): on the weekend (American English), on weekends (American English)

AT

Precise time: at 7 o'clock, at 6.15, at six o'clock, at 10.30, at two p.m.
Night: at night
Specific places: at school, at Roppongi Hills, at Starbucks
Weekend(s): at the weekend (British English), at weekends (British English)

TO

We use with verbs that show movement such as go and come.
- He goes to college at International Christian University.
- She returned to Walmart.
- They are coming to the party at Velfarre.

Kenneth Beare
"Preposition Use - in / at / on - prepositions of time and date"
English as 2nd Language
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(September 26, 2004)