Re: addressing a letter
Welcome to Using English.
The Postal Service prefers that the city, state, and zip be on the bottom.
Whether you do ...
Attn: John Smith
... is your choice.
If its a large company, it's easier for the mail room to see the person's name at the top.
I hope your actual letter uses capital letters and punctuation, though.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.