A preposition links a noun, pronoun or noun phrase to some part of the sentence. Prepositions are always difficult to learn therefore you should practise using the prepositions with the correct phrases or nouns.
Here are few examples of on, at, or in:
On  – to show a surface of something
   I  put my phone on the table.
   Don’t  leave any important papers on your desk.
On  – to show exact days and dates
   The  bar has live bands on Fridays.
 He  was born on the 13th of June 1968.
On  – to indicate using a device or a machine.
   He  is on the phone at the moment.
   Sarah  does all her designs on computer.
   The  cup final will be shown on TV.
On  – to show a part of the body.
   The  ball hit me right on my head.
   She  has a ring on each finger.
On  – to show the state of something.
   The  coat I bought was on sale.
   The  engine was on fire.
At  – to show a point in time.
   I  will meet you at 6.00pm
 The  train leaves at 9.00am.
At  – to indicate a place
   There  is a bus stop at the corner.
   There  were thousands of people at the concert.
   I  live at the end of the street.
At  – to indicate an activity
   I  am good at explaining my ideas.
   They  laughed at the proposal.
In  – for general times of the day, month or year
   I  always have a good breakfast in the morning.
   It  is too hot in the summer.
 I  will move to Madrid in October.
In  - for a location or place
   John  lives in a quiet street.
   I  live in Greece.
In  – to indicate a shape, colour or size
   They  decorated their house in warm pastel colours.
   The  fans waited in a queue.
   Do  you have that dress in my size?
Lesson by Tristan, teacher at EC Malta English school
Now complete the following with the correct preposition: