[danslak]

When addressing the letter, always use "sama" not "san". This is very important! Sama is much more polite and is expected. Few outside of Japan seem to know this, so it might give you the edge you need. So, say you're addressing the envelope to Hisao and Aiko Yamada:

Yamada Hisao-sama
Aiko-sama

Or if for the whole family of Hisao Yamada:
Yamada Hisao-sama gokazoku ichidou-sama

For cultural reasons I'll never understand, most letters start with some mention of the changing of the seasons or weather in general. Here's one I get a lot: "As it becomes warmer with each rainfall, I hope everyone is keeping in good health." --Hitoame-goto ni atatakaku narimasu ga, mina-sama okawarinaku osugoshi no koto to zonjimasu.

Then, "This is the first time that I am writing to you."-- hajimete otegami o sashiagemasu. I know, it sounds weird, but more often than not, first letters are put this way.

End it with: "please forgive my terrible handwriting and poor grammar" --ranpitsu ranbun 0yurushi kudasai. (yes, a personal hand written letter will go farther in Japan than a typed one).

Then, a final ending might be: "Keigu"--respectfully yours.

PLEASE try to write in at least some Japanese. It will go a very long wayf!

Good Luck!