I'm wanting to train my horse to jump, but he's not in the best condition. He's been riden on and off for the past 5 years, and hasn't been ridden at all hardly in the past 6 months. I'm not sure the conditioning I need to get him in jumping shape.
If this horse is really out of shape, start with walk/trot, more walk than trot for 10 mins, then once he's built up some stamina you can move to about 50/50 for about 20 mins, then add some canter in... you get the point.
Start with ground rails first to just get him to realize where his feet are... then I would work with crossrails for a while to make him jump in the center of the fence. You want to work on getting in the box at lower heights.
Once you're both comfortable jumping about 1' to 18" and consistently jumping in the box, then you can move up.
Like everyone has been saying you need to start slow. Start with easy rides for a short time and get him to where he is doing nicely on the flat. Then start working over ground poles in both dirrections. Once he gets comfortable with that start troting a crossrail. Then start jumping small lines and courses. Hill work is very good for strengthening a horses muscles. It will really give him nice strong butt and hind leg muscles which will greatly help his movement and form over fences.