There are a lot of issues that could be going on. Usually with horses rushing fences, pain and/or anxiety are the culprits. If you rule out pain I would try and pinpoint what it is that's causing him to rush. First of all, how is his flatwork? How is his balance at the w/t/c? Are you able to adjust his speed? -This is pretty key! If he doesn't do any of these things well you need to build that part of his foundation so that when you go to a fence and say woah, he knows what you're talking about! I got a prospect several months ago that was a major rusher. He would either rush the 2 strides in front of the fence or take off on the backside of the fence. Yikes! It was not fun.
So this is the program I started with him. I taught him:
-how to move off my leg (not just "faster", but away from my leg as well so he could learn that my leg was actually an AID)
-increasing and decreasing speed, and maintaining whatever speed i left him at. If i say woah, he slows a little until i say go, then he picks up the pace until I tell him otherwise.
-lengthening and shortening his stride. Exercises like lengthing down the long side of the ring, shortening down the short side, etc.
-balance/using his hind end- starting to go on the bit and a few exercises like a shoulder in that really encourage him to strengthen, balance, and use his hind end.
To me, all of those things are "basics" that a good jumping horse should know to be able to be adjustable on course. It also makes jumping much MUCH easier on them when they are balanced, fit, and trusting your aids!
When (or if) his basics are down, I'd keep doing lots of poles and gymnastics (how is he to those?). Lots of horses are anxious about jumping because they "don't know how". Figuring out how to place their legs and what to do with their body are sources of anxiety! Start off with lots and lots of poles (singles and combos. trot poles are spaced 4 ft apart for the 'average' horse, canter poles should be 9ft). My favorite gymnastic exercise to start off (and teach a horse how to canter a fence) is:
ground pole (9ft space) crossbar (12 ft)crossbar (24 ft) vertical or crossbar to start off.
basically you trot in, bounce, you have one canter step to the jump. The spacings I've given you are for a horse with a 12 ft canter stride. I personally think 12 ft is a little big for the 'average' horse. if it's too big for your horse, bring them in a little so it's easier for your horse.
Don't know how high you're jumping him but I'd keep the fences low for now. I personally (and I know there are other very effective trainers out there who think differently) think it's so much easier to teach a horse to jump a course of small fences, and then raise the height instead of getting them jumping 2"6 singles and then start jumping courses at that height.
Here's another thought... i've noticed A LOT of people with horses that are a little fast think, "i'll get a really nice slow pace going from the corner so they'll keep that slow pace through the fence/line". the problem is, every horse has a speed that is most comfortable for them. if they are underpaced to that fence, it's uncomfortable and even difficult (causing anxiety) which cause them to rush either before or after the fence. Which just causes the people to try and slow them down more, which causes the horse to speed up more, etc. I've actually worked with SEVERAL horses lately that were 'rushers' that were 'fixed' by allowing them to canter at a decent pace out of the corner!
Those are the tips I'll start off with. If you have more details about how far along your horse is, what he knows, what he doesn't, etc etc I can offer some more exercises or ideas.