This is a sample of a general letter. This letter will make you understand how you should write a general letter

From
[your name]
[Street address]
[City, State, Zip Code]

To
[Receiver's name]
[Designation]
[Organization]
[Street address]
[City, State, Zip Code]

Dear [Receiver]

As i have gotten a transfer to New jersey, i am moving out of your apartment. We will be moving out of the above mentioned address by December 30, 2008. I have attached with this letter our initial rent agreement, according to which i am supposed to give you a notice 1 month before the time i move out.

I would also like to tell you that, I and my family had a wonderful time staying in your apartment.

If there are any formalities or clarification to be done, do contact me.
Thanking you

Sincerely,
[your name]
ENCL: A COPY OF THE RENTAL AGREEMENT.