I still have a few doubts. Thank you very much.

Question

1) When I go to a party, I generally wear clothes which are smarter than the ones I wear for school.
2) I want to be original and on fashion (is it possible?)
3) What do you think of/about this coat? Are both "about " and "of" possible?
4) I think it is very important to be comfortable because I have to spend a lot of time at school. In the other cases I think it's more important to look cool because I really like being on fashion (wearing fashionable clothes/are both possible??)

Answer 1

1) OK

2) I want to be both original and in style.

3) What do you think of/about this coat? Are both "about " and "of" possible? <~~yes

4) I think it is very important to be comfortable because I have to spend a lot of time at school. At other times, I think it's more important to look cool because I really like being in style.

Answer 2

PS -

You can say that a particular jacket or shirt (or any other article of clothing) is "in fashion" but people are not in fashion!! And "on fashion" is never used.

And if you think "in style" is too cumbersome, then just say "it's more important to look cool / to be hip / to be in.