1. A French Informal Letter Paris, le 16 août 2010
When writing an informal letter it is customary not to include either your own or the addressee’s address.
In this type of letter, people often write the name of the place they are in, followed by the date at the top of the page, on the right. The place is the town, city, village or other recognizable location.
In writing the date, the day number is preceded by le.
Note also that in French, unlike in English, names of the month are not capitalized. The convention is to write dates: day-month-year.
More informally you can write this information in numerals:

2. Greetings
In informal letters or when you know the addressee well, an opening following cher/chère or mon cher/ma chère is appropriate:
Cher Matthieu, Chère Béatrice, Chers Béatrice et Matthieu, Chers tous, (Dear all,) Mon cher Papa,
Ma chère Béatrice,

3. Goodbyes, go on the bottom left of your letter and are followed by your name (on the next line).
With warm regards
Chaleureusement,
In friendship
Bien amicalement,
Your friend
Amitiés,
Best wishes
Meilleurs pensées,
Yours,
Bien à toi,
Affectionately
Affectueusement,
( never from a boy to a boy)
Best wishes to all
Bien des choses à tous,
Love / With love
Je t'embrasse,
Lots of love
Bons baisers,
Hugs and kisses
Bises !
Lots of hugs and kisses
Grosses bises !
(never from a boy to a boy)

4. Other useful phrases Well that’s all! Voilà! C’est tout.
Write to me soon
Écris-moi bientôt/vite.
That’s all for now
C’est tout pour l’instant.
I have to leave you
Je dois te laisser.
I look forward to hearing from you
J’attends ta réponse avec impatience.

5. Addressing the envelope
Your return address should be written on the back of the envelope (althought it can be written on the top left as well) after the word: Exp. (short for Expéditeur/-trice “sender”). An example would be along the lines of:
Exp.: Sarah Fowler
350 N Arizona Ave
Chandler, AZ 85225
USA
There are NO punctuations anywhere in a French address!

6. The address itself
Some people prefer to write the recipient's last name in ALL CAPITAL LETTERS, but it is not necessary.
Lines from the street address down are supposed to be in all capital letters
The French postal service prefers the WHOLE address in CAPS-name, last name, street, city, country)
Madame DUVAL
27 rue Pasteur
14390 CABOURG
FRANCE
[Name]
[street address (house/building number street name)]
[postal code + city]
(You may precede the postal code with
France's country code and a
dash, e.g. FR *Do not use both)

7. Examples More Details:
More Details:

8. Examples

9. Current French “Timbres” Stamps
                                                                        

10. Letter requirements
Location, date (on top right)
Greeting
Body (remember MINIMUM 5 Qs + 5 facts about self)
A phrase to wrap up letter
Goodbye
Sign name
DEVOIRS: Re-write letter on nice paper, put it in an envelope, address the envelope, draw stamp.