Laying-on is a wonderful technique when fishing slow to medium pace rivers. It's both a visual and subtle way of catching fish that can be shy biting. I like to use small shot as my bulk (number 4s are ideal) normally around 8" to 12" from the hook. Then depending on flow rate a float fished some two feet over depth. If the flow is modest a 6 no 4 stick float with a shoulder would be my choice for chub and barbel.
It's both a visual and sensitive way of fishing for many shy biting fish. There is nothing like watching a float glide away, knowing some fish has fallen for your bait. I'd much prefer to watch a float than a rod top or quiver tip, I also think the resistance is less with a fine float.
But sometimes when the river is up and swollen you have to use a bigger float, something like an Avon, with a cork or balsa body allowing more shot. At a time like this finding a slack or crease away from the main flow can be better than the main flow, unless your after barbel. Then right under your own bank-side with a big bait like worm or meat can work. It's amazing how many big roach I've taken at times like this laying on in slack water. As long as it's not collecting rubbish it's fine.
When long trotting in summer for barbel there are times the swims dies, as if all the fish have moved off. But by pushing up the float and laying on with a still bait can work wonders. ( This was a great tip given to me by a friend called Steve. He catches a lot of big barbel like this, and I'm going to use it more when trotting slows down.) I think it's just the fish are collected and not intercepting a moving bait anymore. In another hour with constant feeding it can all change again.
Typical selection of river floats.
It works for most river species. Big perch are suckers for a big worm fished under a float, as are huge roach. Years ago when I fished a small river in Leicestershire big roach would appear after a flood in many of the slacks. We would fish large porcupine quill floats with worm or maggots as the bait. Fish that would never get caught during normal conditions, would put in an appearance. Fish over 2 lb being caught during high water.
If you've not tried laying on give it a try, you may be surprised. You won't get that crick in the neck from looking upwards at rod tips all the time!