I repeatedly hear from wholesalers that direct mail still works and is one of their strongest tools. Given the technological world we live in today, it surprising to me that it still works. But my understanding is that it's a numbers game. Be ready to send a campaign of 4-6 postcards (etc) per potential lead before you get a response.
I agree above with the Micromarketing strategy. Get really intimate and familiar with an area, personalize your approach. This has worked for me numerous times over the years. I bought a home from a seller once who I had sent a handwritten letter to 9 years earlier to his mother. After his mother's passing, the seller (son) found the letter in a drawer in her home and called me. So it works!
Lastly, there are great tools like DealMachine etc that allow you to "drive for dollars." This makes prospecting much easier, as you will have all the owner contact information at your fingertips. You can even send a postcard immediately from the App. BTW: I have zero affiliation with Deal Machine... just saying it's an app thats worked for me. There may be better/different ones out there.