All I do is cast out with the line clipped up and as the rig flies through the air, I hold the rod with the tip pointed vertically.
This serves two purposes. Firstly, if I hold the rod in the same position every time I can be sure that the rig has travelled exactly the same distance at the point it hits the clip. Also, the force of the rig pulling the line tight against the clip is absorbed by the rod bending. This protects the line in the event of an over zealous cast.
Once the rig hits the water I unclip the line from the line clip and allow line to leave the spool freely. I want the rig to drop through the water without being pulled offline. I feather the line using my finger on the lip of the spool. This prevents tangles. I find that heavy monos (10lb plus) are quite springy and if left unchecked will jump off in coils. This is why I prefer Krystonite. It's the best behaved line I've used.
As the feeder lands I allow the flow to pull more line from the reel (again, while feathering the spool). I let out around 15ft feet of line which creates a bow.
The bow means you will be able to hold bottom with less lead. This is because there is less pressure on the line because of the angle and because it has more give than if it were tight. The line near the rig will be pinned down and this means that the Barbel are less likely to notice to be spooked by it.
If you?re fishing two rods (I always do on the Trent) you need to watch how the line sits in relation to the other line and rig on the other rod. You need to ensure you can land fish on either rod with disturbing the other. If you?re not sure, fish with one rod at first.
Because of the bow, when a fish takes the bait it should dislodge the rig and this will show as a drop back on the rod tip. Ideally you should strike before the rig settles again. I find the fish are more likely to hold onto the bait because the hooklink is slack while the rig is moving.
You'll find that Barbel will often bolt as the rid resettles and the hooklength tightens, but this isn't always the case.
Bream will often sit there sulking - even the big ones. Many a time I've reeled in for a recast and found a Bream on the end. At that point I will remember the knocks I'd had twenty minutes previously!