So write your story as it needs to be written. Write it honestly, and tell it as best you can. I'm not sure that there are any other rules. Not ones that matter.
Let us begin this letter, this prelude to an encounter, formally, as a declaration, in the old-fashioned way: I love you. You do not know me (although you have seen me, smiled at me). I know you (although not so well as I would like. I want to be there when your eyes flutter open in the morning, and you see me, and you smile. Surely this would be paradise enough?). So I do declare myself to you now, with pen set to paper. I declare it again: I love you.