What to write in an award nomination letter about your supervisor? An international society is accepting nominations for an yearly award for young principal investigators in our scientific research field, and I would like to nominate my supervisor.

I have to write a nomination letter about him.

The rules about this letter state: 


  "Your personal assessment of nominee's contributions to our scientific
  research field deserving of this distinguished award, including major
  scientific contributions, up to ten references to publications, and
  other contributions to the field that demonstrate this nominee is
  deserving of this award"


I never wrote such letters so I don't know how to start...
I think I should start by talking about the deliverables (scientific softwares and papers) he released in his career, and their impact in our field. Is this correct?

Then should I acknowledge about his career achievements as well?

Should I call attention to the quantity and quality of his publications (e.g. "He published many papers on Nature journal, etc")? 
Should I mention the other awards and honours he got in his career?

What do the scientific award organizers want to read in my letter?

I want him to win!
I am guessing you are writing this because you want to nominate him and you have had interactions with no one else that is writing for him or nominating him.

Typically such letters for discipline-wide awards are written by senior members of the academic community, unless explicitly stated in the call for applications that very junior researchers are supposed to do the nominations. Very likely what will happen is someone will see that you are his student and consequently write off your application for your advisor as a conflict of interest. If you are nominating your advisor for an award based on their research level and you are a graduate student, chances are it is not going to hold the weight that other letters will have and they will pass over your nomination.

This being said, if your letter is in a bigger file of people writing in support of your advisor, then it will carry some weight. If you are applying with a group of people that are nominating your advisor, it has a shot. If you are doing this, I would focus on the other contributions aspect of the call.