Some of the best fishing can be in winter; equally, some waters can get almost impossibly hard. You may have to get up early to get a peg on some Wye stretches, the winter fishing is so good. Meanwhile, you can have a mile or two of river to yourself where I live.
The general advice about locating more tightly shoaled fish, feeding them more cautiously, and expecting shorter feeding spells later in the day is definitely right. And there's no substitute for having a walk around to look, asking locally and testing it for yourself.
There isn't always an obvious answer to winter conditions; sometimes the fish are just less active and the fishing less productive. I was out yesterday, with an FM member who certainly knows how to catch fish, on a stillwater we've fished a couple of times in the couple of weeks since the latest floods and first hard frosts kicked in. We've spoken to the bloke who runs the fishing, chatted to bailiffs and gamekeepers. We've walked round and scrutinised all the pegs from the point of view of wind direction and - it's in woodland - how much sun will fall where and when. Between us we've tried half a dozen pegs, waggler, pole and tip at all kinds of depth and distance, and maggots, pinkies, flake, crust and corn. Yesterday, neither of us could get a bite between 10 am and 12, and the flickers of life between 12 and 3pm got us a total of a dozen bites or so and 5 fish between us. The contrast with the fishing before the weather changed is huge, and if there's a trick to catching more at the moment, we couldn't find it. It was still enjoyable fishing, but the fish appear to have switched off.
On the brighter side, if you get into fishing natural waters in winter you'll find fewer others around and a special kind of pared-down beauty to the waters. By the time we get to December and January, expectations get adjusted and any bit of success is appreciated. There are a couple of little rivers nearby where, if I go out at 2pm and fish til 4pm, I can get 2 bites and a chub, or even, on a red-letter day, 3 bites and 2 chub, and come home feeling like that was a good day's fishing!