To the unknown reader,
While choosing a postcard, try to think about your favorite quote/expression or one of your weirdest dreams and write it down on the card.
I'm fond of photography and I'm attaching pictures taken by me to the postcards I send, sometimes.
Most likely I will enjoy the postcard which can surprise me, less likely it will be a touristy view card.
The best way to become boring is to say everything" ;)