Did you know that we have different rules to write business letters in English depending on the person person are you are addressing? In this post I suggest you to have a look at this website (mainly for native speakers, but also useful for us : http://www.writing-business-letters.com/). You could find on the Internet even templates like the very practical ones at Microsoft: http://office.microsoft.com/en-us/templates/CT101485751033.aspx (Just download and edit) .
Try to have a look and read them! After that, tell you about them here! Did you find them interesting? Did you know of their existance before? Have you ever used a template?
You could even use a writing generator!
Have a nice writing...;)