Fun rides are good - I used to do loads with my friend's cob, plujs you get to jump all sorts of different things which makes them bolder. Try to find some hacks where you can trot and canter up hill, and hack out with someone else so that he is more forward going. Find out if there is any autumn hunting happening near you - this is brilliant for lazy horses, and is cheaper than when the season proper starts.
They need to go forward and flow so make sure you get a really good canter before you start jumping at home, and try to avoid pulling and looking for a stride too much.
Some shows will just use rustic fences but they will often be filled and surrounded with greenery so get him used to this - beg some Lleylandi clippings from a gardener or look for fallen leafy branches to practice with.
Steering's important too as most courses include a stile and you might come across a water tray - if you haven't got access to a range of fences it's worth hiring an arena that has them. Enjoy - WH is great fun!
Start by getting him properly fit, lots of walking out hacking, hill work and basic education to have him responsive so he is less lazy, you can then do the schooling required and begin jumping to get him prepared for next season, go out to do clear round jumping once he is ready, hunt in the winter if you can/ want to and some hunter trials, all this will give him a good preparation to do any job, which is what a working hunter is really, a good all rounder.