Put your main message or a summary of your document first, after the headline. In fact, the very first 6 words should give a strong clue about what's in the document.
Assume other people will read only the first line or two of your document and not another word. (Much of the time, that's the truth.)
Will they discover what your document is about? Will they get your main message? Or will they just read some introductory thoughts? If so, all your work is wasted, because many will read no further.
This basic rule of plain language applies to nearly all business writing. Even if most of the information is listed chronologically or in sequence (for example, in instructions), you should still put a summary first.
Exceptions include opinion articles, bad news letters and letters of apology.