let me help you out! For Ref.

No particular format for NIW petition letter.
Typically it should include following things:

1: greeting to immigration officer

2: the purpose of your application

3: decription of your achievements chronologically (something like your personal statement) to demonstrate you are superior to the peers in your area, Americans and foreigners.

4: address your work in terms of national interest (i.e three criteria for NIW, with citation from recommendation letters to support your claim)

5: list of all your supporting documents.

There is no particular order in items 3, 4 and 5. It's up to you.