A Postcard backside consists of two areas, one for a greeting or personal message and one for the address and stamp of the receiver. You can draw these lines and areas yourself, or use my free printable backside and glue it to the back of your artwork.
I think you should always add in a Greeting.
Your contact information.
And don’t forget to add the right amount of Postal Stamps.
Some people participate in other swaps and exchanges, and they greatly appreciate if you stat what swap this is from: the iHanna DIY Postcard Swap + year.