In reply to Bouldering8mad: Apart from the obvious "climb more" (I'm sure that brigade will come along soon, and maybe will one day realise not everyone lives 5 minutes away from a wall/rock) I've found powerballs to be really good. They're £15ish on amazon, and you can use it whilst cooking/watchin tv/anything else you can think of that only requires one hand.
Just remember to swap hands every now and then. And they only work if you work them hard. You're arm should feel like its about to fall off when your done.