Hi Dan
I usually walk from Sheung Shui KCR station. Walk north from the station on the same side you come out, under the underpass where it crosses a main road, continue north past the industrial estate (if you cross the road here you can walk alongside the river), cross the river at the footbridge and continue north along a concrete road. The Long Valley fields are to your left about half a mile along this road, you can enter the fields wherever you please.
From here walking west you cross all the Long Valley fields and eventually end up at Yin Kong village, walk through to the main road and take a taxi back to Sheung Shui. Alternatively, walk back the same way you came.
You can wander where you like over the fields as long as you keep to the bunds. The best fields are often the unmade ones at the Yin Kong end but you can find birds anywhere.
I am a vagrant now at Long Valley, someone else can tell you where the good birds are.
