Also, it's not enough to have lists of expiring domain names. You also need multiple connections to the registry to compete.
You're a bit late to the party to be at the stage of asking how is it done.
Party over.
Anyone with a different perspective feel free to beat up on me. Now is a good time as I'm a bit exhausted from navigating the ICANN debacle. :-P
But, for the most part, the big registrars grab expired domains, so it's mostly too late to get in on that game anymore.
Though I did recently have success re-getting one of my own domain names, which I had overlooked renewing. I used GoDaddy's backorder service, and the domain was registered through a different registrar.
Initially, it failed to capture it. But then a couple days later, I got a message that capture was successful. Weird, but it's mine again.