The process of lungeing is often misunderstood and done incorrectly therefore the benefits are not recognized and is often disregarded. Yet it is one of the most crucial parts to training the horse. Training starts from the ground up. First step is the horse should know the simple voice commands, whoa, walk, trot, canter. These can be taught in a round pen with or without a lunge line.
Your lungeing equipment should be a good quality surcingle, side reins, a long lunge whip and lunge line. I prefer the Rebalance sliding side reins. These side reins allow the horse to stretch and travel through the topline and come up into the contact in a balanced way.
The purpose of lungeing your horse is to warm up, connect them, and get them traveling properly before mounting. It is the precursor to riding. Everything that you do on the lunge line mimics what happens under saddle. If your horse cannot lunge properly, making a round circle, traveling forward from the hind end to the front and connecting to the contact in the bit and lunge line then under saddle you will have the same difficulties.
Stand in the center of your circle. Your horse is to go around you, you are not to walk around in a circle with your horse. Then the horse is lungeing you. The horse is not to blast around on the line, they are to travel in balance on the contact in each gait. If you are riding them and they are not forward, in front of your leg, the response is to use your seat and legs to get them more forward. On the lunge line, you snap the whip behind them. This is the same thing as using your legs and seat to drive them up.
Think of your circle as a pie. When you slice a pie it makes a triangle with the crust at one end and the apex in the center of the pie. You are the apex and your horse is the crust. This should remain this way the entire time you are lungeing. This position places you at the girth. If the horse is lazy and not in this pie section, you will no longer be the apex, they are behind you. This is the same as being behind the leg when under saddle. You would ask them to come up in front of your leg by using your seat and leg. On the lunge line, you will use the whip to do this. Once they are in the proper place on you pie, you no longer use the whip.
You must maintain the positioning of the horse and yourself in the slice of pie during the lunge session. If they are too quick and get ahead, you need to half halt on the line the same way you would under saddle. They also must be bending around the inside leg, but you are not on them so how do you do this? Stay at the apex of the slice of pie, this makes the horse have to bend and make a circle around you instead of traveling crooked while you move all around the place. If they fall in, you push them out by pointing the whip at the girth. This again is the same thing you would do under saddle, by using your leg. This will move them out on the circle.
If done correctly, when you mount and begin your ride, the horse will already be forward and on your aids and you can progress faster and with less effort in your training. The horse develops a nice connection with you as you earn their respect. If you have a horse with training issues, this is a safe and effective way to make corrections and eventually the bad habits get replaced with positive ones.
If you do not know how to lunge, don't do it. Instead get someone who is knowledgeable to do it for you or teach you. Done the wrong way instills the wrong habits and can turn into problems, such as the horse turning in on you, rearing, reversing direction etc.