I also have Grid Square and Latitude/Longitude on my cards, too.
Rather than trying to put everything on one side, and having the other side with address lines, like a post card, I have on
cards I've done for myself and others, picture and call sign on one side, and everything else on the other.
Printed on your card should be your call sign and name,
Address. Put USA under the street, city, state, zip code lines. Do not assume someone in Greece will look at the card
and know it is the USA.
Put your county, Longitude / Latitude, Grid Square.
Your station description, (Ten-Tec Jupiter, 75 watts, Fan Dipole)
Power in watts for the contact. (Was your signal 4-7 using a QRP rig at 2 watts? That would be good to note.)
Your email address.
You want to include blanks for
Recipient's call sign,
Date and Time UTC,
Signal report (RST) Note - you only supply a third digit if using CW to describe received signal quality.
Freq and/or band.
Mode (SSB, CW, RTTY, PSK31, etc)
And a place to check one or the other.
[ ] Pls QSL [ ] TNX
If you sent a card first, you would check Pls QSL (please QSL).
If you are responding to the other ham's card, you check TNX (Thanks!).