You should say:
Who he/she is.
When you became friends.
How he/she influences you.
Why you like him/her.
a) I made many friends in school, but the friend I would like to tell you about is called XXX.
b) I am sure you have a friend like this in your life as well.
a) I met XXX about XXX years ago at the school that we attended together, and we soon became friends.
b) Our friendship has lasted to this day.
a) Our friendship has grown a great deal over the past three years.
b) These days, for example, we share all our secrets with each other.
There are several reasons as for why I would like to talk specifically about XXX as a friend. Allow me to explain by mentioning some of them briefly.
a) I guess the main reason why XXX and I became such good friends, is that we have the same interests.
b) For example, we both love listening to music, and we spend many hours together listening to our favorite CD`s.
a) Another reason why we have become such good friends is that we both would like to go and study abroad in the near future.
b) So we often chat about what possible majors we would study, and what university we would like to attend.
a) A third reason why s/he is my friend is that we share many principles.
b) For example, we both believe that we should not damage our health by smoking cigarettes.
a) Lastly, I believe that XXX has had a positive influence on my life since we have met.
b) XXX is always friendly, cares about his/her family and friends, and is always willing to listen to others.
8. So now you know why XXX is such a good friend.