In reply to wilsers:
Ignore the dispiriting grades, up to the 6s at least they're just randomly sprinkled about with little rhyme or reason. The style also takes quite some getting used which can be frustrating but it's well worth persevering.
Avoid Bas Cuvier like the plague, it may be a crag you've heard of and it may have some classic easy circuits but it's a filthy roadside cess pit.
Work out what you're looking for crag-wise, some are really popular, busy communal places which can be fun, others are quiet, a little overgrown and you're as likely to stumble across deer as other climbers.
Buy a large scale map (tourist office in Font' sells them IIRC) and take a compass, it's seriously disorienting in the trees. Pre-load a sat-nav with all the crags you might want to visit and their parking. Time wasted failing to navigate using the various very confusing books can really spoil a short trip.
Ask around a bit about the crags you're thinking of before you go, some are what we'd call routes on the grit, some have bad landings, some have suffered access problems and some of the approaches/parking shown in the books are now barred fire roads (and have been for at least a decade).
It's pretty spread out, to access a selection of crags you'll need transport. If you haven't got a car then do some bike/bus research before you go.
Navigating is a pain. Finding stuff in the trees can be a pain. What you do find can be pretty dirty/high/hard/crap. When you find the good bits it's totally utterly superb
Enjoy,
jk