It's covered in Beastmaking.
Thanks for the replies. So in terms of the actual exercises people do, is there any agreed ideas on what is/isn't useful? I can see there are various things you can do, from crimp curls in which it's just the fingers that move, to static holds in a range of positions (straight arm/bent/fully locked), to repeated lifting of the weights, all in the various grip configurations. Having played around this afternoon the static hangs with a fair bit of weight felt fairly useful in a specific climbing sense.