In reply to Phil Tucker:
repetition, pick a route, be it glentress, brenin, betws, grizedale, wolf.... and repeat. Several times in a day. You'll learn which bits you hesitated on, over cooked etc... or weren't in the right gear etc.
Skills areas are ok for basic balance, mini skills etc., but a few km of track is much better. It's a bit like skiing, you need a few turns to get into the swing of things, or rhythm. Cover your weaknesses, drop offs, jumps, fast corners/berms... you'll know what they are already.
Good out with a friend who is faster and can tail you down and around stuff, get some feed back on body position over the bike etc..