Postcards are nowadays the best souvenir you can cheaply send to family and friends. It's a cool surprise as less and less people still send them. My tricks are:
Part I: to manage space, put the stamp and write the destination address first. Then you will know how much space you have left to write your message and signature.
Part II: "postcard insurance" - take a picture of the finished postcard before sending it. Keep it on your phone until the recipient receives it. This is nice in case your postcard never arrives, but also useful to track which cards you sent and when. #entertainment source