Study the information about prepositions on, in with other uses.
1. Remember these phrases:
on business
on a trip
on a tour
on a cruise
on holiday
I am going to Portugal on business.
On strike
On a diet
On fire
On the whole (=general)
On purpose
On a diet
On fire
On the whole (=general)
On purpose
John has problems at work, but on the whole, he likes his job.
But! We use by with: by mistake, by accident, by chance
2. Expressions with the preposition in:
In the sun, rain, shade, dark, bad weather
Write in ink, biro, pencil
In words, in figures, in block letters
Pay in cash
Be/fall in love
In someone’s opinion
In my opinion, the concert was wonderful.