we do lots of postcards. thing to remember is you must be persistant.
the first time you send a card it might get tossed into the trash without it being read. so you need to send on a regular basis to the same addresses.
we send every 30 days (or so) most times we dont get a call untill the homeowner recieves our 5-6 mailing. I have asked, on occasion, why they waited until they received so many mailings to call, most say it was the first card they received....which i know is not true...they just tossed the others without reading them and didnt realize we had been mailing them monthly.
its all a numbers game. the more you mail, the more frequent you mail the better the response