French postcards usually only contain short words, especially when traveling, where you write where you are, express your concern for the other person, and write some blessings.
What you want to say is written in a large blank message space. It is customary to put it on the left half of the postcard and there are horizontal lines on the right half of the page to indicate the order of writing the address. Pay attention to the order:
First Recipient's name
Second house number, street name, (or add community name)
Third city name plus zip code
Last country name