Trot sets, preferably over easy hills. If you don't have hills, that's fine too, but it'll take a little longer to get him fit.
Starting off, especially with a pony that's a bit out of work. I would do two 8 minute sets. It would be something similar to this: 8 minutes trot - 3 minutes walk - 8 minutes trot. After that, I would take him into a ring and do a little bit of flat work. As he gets more in shape you can work up to two 15 minute sets and that would be all he would have to do for the day. Incorporate a lot of transitions and CORRECT lateral work into his training as well. If he's as bold of a jumper as you say I'd keep the jumping to a minimum of once a week for now, until he gets into better shape.
"Always be yourself. Unless you can be a unicorn. Then, always be a unicorn."