When I worked under a trainer starting horses to jump, all the horses we worked with already had a good solid foundation of dressage/flatwork. With horses I've worked with off track, or before they were able to jump, at least six months (usually more) was just dressage and flat work, with poles and small cavalettis thrown in occassionally. Make sure this horse is capable of doing a collected, medium, and extended walk, trot, and canter when asked - adjustability is key for jumping. Leads are also important, make sure he knows how to pick up the lead you ask and when you ask. Stopping is just as, if not more important than learning his gaits. Make SURE he knows whoa! Practice stopping randomly throughout your schooling. Get him 'on the aides', as George Morris says. If he is actively listening to your aides the whole time, he is less likely to tune you out and do as he pleases.
Once you're sure he has a good, solid foundation, begin to set up courses with standards and poles on the ground. Have him trot, stop, and canter through the 'course', just as he would have to do if they were real jumps. When the jumps are just ground poles, any problems he might have are less extreme. I also recommend having stride poles set between the standards, like in the picture below (taken from google):
If there is a jump you want trotted, setting up trot poles will help him learn where to place his feet, while not just rushing through. Same for cantering. I like to have stride poles before and after jumps on horses that are learning because it helps steady them and find their rhythm. You can also place stride poles in between lines and at the ends of the arena, to help with half-halting. This to me just reminds the horse to think about his foot placement and, again, not to rush.
After ground pole coursework, begin to raise the jumps. A lot of trainers like to start out with cross-rails because they aren't intimidating to either horse or rider, plus it teaches the horse to aim for the middle. Even when you start to make the jumps verticals, keep an X in the jump for a while, so it helps him keep to the middle. Another neat idea for keeping the horse straight to the fence is adding poles on either side of the jumps as a 'shute' of sorts. People also like to have the shute lead up to the jump itself and put poles resting on either side of the fence, so the horse wants to stay to the middle. My friends and I particularly like to make a 'V' formation with the poles to the horse snaps his knees up better, as can be seen in the picture below of my friend and her pony, Annie:
Free-jumping, or lunging them over fences is another option when a horse is learning to jump. This helps a horse learn how to get over something without being inhibited by a rider. Don't use this to just see how high the horse can jump. Do this with a purpose.
Also, Gymnasics are one of my favorites! They are REALLY good for getting your horse to learn how to really use himself, as well as forces him to fend for himself through a line. There isn't much you can or should interfere with once you've entered the line. Your job is to keep him straight and offer a good approach. Cross-rails in a line are a great place to start, because he is more likely to want to keep straight (google image):
These are bounce jumps, but you could start out with one or two strides in between. Adding a take-off pole in the beginning with stride poles before it can really help to set him up for the line properly. If he takes a long spot at the first jump, the rest of the line may be sloppy. I also recommend poles after the line, too, to help keep him from running off after.
A good exercise to do is jump a fence or a line and halt in a straight line afterward. My current trainer advises against striking a canter on line with the jump if your horse tends to get fast or heavy. She likes to canter or trot a half circle onto the line of the jump and then halting after in a straight line. This way, the horse doesn't associate the up in speed with the jump in front of him.
I hope this helps! Sorry, didn't mean to write a novel xD