When grayling fishing on the southern chalkstreams I expect over 20 fish a session with at least 4 over a pound and maybe one around the 2lb mark. I am puzzled then by the number of anglers I chat to who have either blanked or managed two or three small fish. I don't pretend to be an expert, but my methods clearly work so I thought it might help to describe how I fish.
So far as tackle is concerned, I use a 3 weight rod as long as I can comfortably manage. On the Test, without much tree cover, this will be 10'; on the Upper Avon where it can be a jungle, 7'6" is appropriate. I usually use a furled indicator leader 3 feet long and attach the tippet to that. I use 3lb (0.1mm) stroft and I don't use a long leader, 4 feet is long enough. This is much shorter than most use on the chalk but a short leader gives better control and bite indication. If the fish are spooky then lengthen the tippet, but I would never go beyond say 8'. Sacrilege, but there it is!
The next consideration is whether to fish a single nymph or a duo rig. On those beats that are single fly only the decision is made. Otherwise, consider the pros and cons. A duo (dry fly on a dropper, nymph on the point) will give great bite indication, it will slow the fall on the nymph and make it much easier to fish slower water, and it will give the opportunity to pick fish up on the dry (though the bigger fish will come to the nymph). On the other had it's more prone to tangles and with varying depth, the nymph can be held above the heads of the grayling. I will often start with the duo then see how it goes.
I use small, heavy nymphs. I often see people fishing with size 12's. Might work for them (but usually doesn't) but I wouldn't dream of it. I use size 16/18/20 PTN or hare's ear with a 2mm tungsten bead to get the fly down to the fish. Use the 18/20 a lot more than the 16, I've had plenty of 2lb grayling on size 20 PTN's.
Essentially we are looking to fish the deeper water because this is where the fish hold. It doesn't need to be much deeper, an extra foot is ample. So look at the outside of bends in the river. Look for gravel gaps in the weed where fish hold. And fish fairly short, I rarely fish more than 2 rod lengths away from me. If wading is allowed, then wade (quietly). It makes it much easier to achieve a drag free drift. Keep moving! I sometimes see somebody in the same pool for a morning not catching fish.
There we are, hope it helps somebody!
Peter writes a great blog Walks and Fishes