What I do is I attach long lines (in my case, two lunge lines) of different colors onto the bit. I have always used a saddle for ground driving, it works best for me (I can stand surcingles). I run the long lines through the stirrups of the saddle and stand well behind the horse. I like to use two different long line colors so that I can easily figure out which is my right rein, and which is my left. It really saves a lot of confusion, because ground driving tends to be a lot more hard for the driver to figure out than the horse!
I will already have taught my horse to go forward when I cluck by round penning. To do this, I let the horse loose in a round pen, then point which way I want him/her to go. I cluck, and if he doesn't move off right away, I smack the ground with a stick and string or lungeing whip, then smack the horse if he still doesn't move. Once you get the horse to the point where you can point and cluck and he moves off, he's ready for ground driving.
I like to start in a round pen or other rather small area. Standing behind the horse, cluck to get him moving off. You may want to stand slightly to the side in order to avoid getting kicked. When you want to turn, pull on one rein and push the indirect rein against the horse's side. If he doesn't turn, you can slap the direct rein (the rein you're pulling) on his side--just be careful not to jerk the bit. It's a good idea to teach your horse to give to pressure before you begin--do that with lateral work. Pull one rein around to the horse's side, and wait until he gives--releases the pressure by creating slack in the rein--then release. You can then teach him to turn by holding the rein and tapping his flank, and when he moves away, stop the tapping, wait for him to stop moving his feet and give to the bit, then release. Do both sides equally.
To stop, seesaw the reins--first one, then the other. Some horses rear up when introduced abruptly to pressure on both reins (I have a pony I'm breaking who does that). To back up, seesaw the reins very gently, and when your horse takes one step backward, release the pressure, give him a break, then repeat.
Keep your lines organized. This is probably the most difficult part of ground driving! Above all, stay safe. If you run into trouble, get a trainer or knowledgable friend to help you. Or, you can practice on a well-broke horse who will probably understand your mistakes a lot better than a two-year-old.
Good luck!
