Leith Hill is quite large and rambling compare to other bits of Surrey Hills- as a kid I remember being baffled by it. Often you will lose track of which way it is back to the top, let alone where all the stuff is. Best thing would be to tag along with some riders – maybe turn up at Nirvana Cycles in Westcott (be nice to the locals, park a little way away and ride to the village) – or maybe get yourself to the top of the hill and ask other riders.
The Summer Lightning trails are easy enough though go to the Plough at Coldharbour, then down the byway opposite (Wolvens Lane) – trails are on the left.