If you are writing a letter of complaint, give all the relevant information that has lead you to complaining.
Before you end your letter, refer to any attachments that you may be enclosing so that the reader understands why they are there:

I have enclosed a copy of my resume, which provides further details of my employment background...

I have enclosed a copy of the document in question...

Your final paragraph should invite your reader to contact, indicating what action you are seeking.

I would welcome a chance to further explain my case at a personal interview...

I look forward to your immediate attention to this problem...

The final part of a business letter is the CLOSING.
Always close a business letter in a professional manner.
Use such closings as "Yours sincerely,", "Yours faithfully,", or "Sincerely yours,".
Be sure to leave 3 blank lines between the "Sincerely yours," and your types name, because in between those you will write your signature.
Also remember that you can type your job title under your typed name.

Yours sincerely,

Joe Bloggs

Manager

Finally, your business letter should be folded in three by folding the bottom of the page two thirds of the way towards the top, then folding the top of the page downwards. The letter should then be inserted into a business-sized envelope and clearly and neatly addressed. liuxuepaper.com