I'm not a huge expert, but I'll tell you what I know.
The approach is one of the most crucial parts to jumping, although it may not seem like it. It makes all the difference to striding, distance, safety, and success. To perfect your approach, pick up a trot or canter. Give yourself some time to establish an even, steady pace. As you approach the turn towards the jump, look into the turn, but hold back with your inside leg until you are lined up directly to the center of the jump. You should see a straight line from you to the center of the jump to a spot on the wall at the end.
Once you are lined up, keep your inside leg on and use your inside rein to bend your horse towards the jump. If you must, use your legs to straighten out your horse. You may start to feel him begin to veer to one side or shift is weight. Act quickly to avoid a refusal by applying steady pressure with the opposite leg.
Make sure you are sitting back so that your horse can properly gage his distance. If you are leaning over your horse's shoulders you are interfering with this process, which could end up with your horse taking off at a long or short spot and you overjumping.
When you are several strides away, squeeze firmly with your legs. Jam your heels waaay down if they are not already (which they technically should be). If you are approaching at a canter, count your strides in, either out loud or in your head. Look straight past the jump to a spot on the opposite wall. DO NOT look at the jump, even during the approach. Where you look is where you go, and you do not want to end up on the ground.
Last but not least, WAIT FOR THE JUMP. Do not get into jumping position before your horse takes off.
When your horse takes off, he will tuck and jump and the upper half of his body will rise into the air. It is your job to meet him there. As your horse takes off, you must fold in jumping position. That is, move your hands up his neck (and grab a bit of mane if you need to), lift your seat out of the saddle, and close your hip angle.
To avoid over jumping, stick your butt out a little. Keep your back straight or with a tiny arch in it. Look UP at your spot on the wall (or your next jump, if it's a double). And jam those heels down! If you often find that you get left behind, grab a tuff of mane as you go over. It's better to pull on the mane than to pull on your horse's mouth.
While in the air, give a squeeze/jab with your outside leg to encourage your horse to pick up the right lead after the jump. If your horse has trouble getting leads, you can also lighty tug the inside rein, but don't cut your release. Keep your eyes up and look ahead.
As you land from the jump, gently sit back into the saddle and bring your hands in. Ride straight to your destination. If it is your last jump, finish off with a circle before letting your horse break stride. Never let your horse rest until you are finished with a circle, because he needs to know that he has to keep going until you allow him to stop. You don't want him stopping in a show.
Anyways, I hope I was helpful. Good luck to you and your horse.
And to BlondieHorseChic:
Your 2-point over the jump should be the same, regardless of whether the horse is green or not. However, on the approach, make sure you sit back and ride in complete full seat (if you canter). You must also help your horse over the jump. If he is learning, he will not be push-button. He needs all your help to get him over. Use all the nescessary leg and rein aids, and you can never stop paying attention.
Practice over trotting poles also to practice your 2-point and striding.
Good luck to everyone. :)
-----In riding horses, we borrow freedom-----