In reply to gazfellows:
Hi,
From your profile you are clearly an experienced climber already, perhaps with mainly single and some multi-pitch routes. I would suggest you already have a lot of the skills needed for big walls.
Start off by doing many more multi-pitch routes and get those skills really slick; building belays, belaying, ropework, swapping over at belays, leading through, one person leading multiple pitches in a row, not getting the rope(s) in a mess etc.
At the same time pick some short, quiet venues where you can learn some aid climbing and ascending / jumaring skills on well protected single pitch routes to keep it simple. Vary the routes from slabs to steeper faces, overs roofs and across traverses; all require different skills. Then add in learning how to haul a light bag up the same routes, that will add a totally new dimension. There are lots of books and on-line resources to help.
Practicing a lot will make the above much more automatic when on a big route and tired etc.
There's loads more I could say, but that is plenty to get going with.
Have fun.