Fishing for thornback rays is invariably a waiting game. Having located a good mark, you should be prepared to cast out or drop back your baits, and then wait. Of course, sometimes you will catch fish almost immediately, while at other times it will take some time for the fish to respond to the combined scent trail of several baits washing downtide.
The key when targeting thornbacks is ensuring that at all times the bait is fishing stationary and hard on the seabed. The thornback is a lethargic species of fish, and are not inclined to actively chase after their food.
When you do get a bite it is important to remain patient, and give the fish plenty of time to shuffle its way on top of your bait in order to eat it. Trying to set the hook too early is probably the biggest reason that most ray bites are missed. Usually, it is best to wait until the rod starts to bend as the fish, having taken the bait, attempts to swim off, at which point you simply set the hook by firmly lifting into the fish.