There are three main sub-species: bullheads, channel, and blue. If you're looking for a big cat, you can ignore bullheads. Most only grow to a pound or two. See below.
That leaves channel and blue. In order to target those bigger cats, the first thing you have to do right is the time of day. Catfish will bite at any given time of the day, but their activity increased a LOT during the wee hours of the night. With a moon like the one below, you won't even need a flashlight!
Next up is the bait. If you want to avoid the little bullheads, stay away from using worms. Instead, I would use one of four baits: hotdog weenies, cut bluegill, cut shad, or cut carp.
I'm a BIG fan of hotdog weenies. There's a separate post on here that will show you how to put them on the hook. Bigger catfish seem to hone in on them quick enough to beat their smaller counterparts to the dinner table. Case in point.