This is the time to break out that living room driving partner, the rein board. A rein board can be as simple or as well-built as you like. You can create a very simple rein board just by throwing a pair of reins over a dining chair and then tipping the chair away from you, using the reins to keep it from falling to the floor.
If you are feeling industrious, you can build a rein board yourself out of a saw horse, a couple of pulleys, a set of reins and some sort of weight. I'll advise you to avoid using two separate weights for your reinboard. If you do, the reins do not act in concert the way they do when they are on your horse. Instead use a solid bar, or hang weights off of a bar bit of some kind. That way you can really feel what the other rein is doing.
Of course, if you really would rather someone else engineer the whole reinboard assembly for you, you could simply buy one from us. We have a few on hand, and would be happy to send one out to you!
To start with, this is the perfect time of year to develop your hand's understanding of the various rein positions that can be useful to you as a driver. Take a look at the article "Driving from the Left Hand" in the Coachman's Guide. There are some pretty clear illustrations there on where to put the reins. What's not illustrated there is the riding position. I'll work on getting those pictures up in this article for you.
It will take at least one or two sessions to get your hands to hold the reins in all of the different positions that I've shown you. Take the time to get these positions down, and get them right. You'll probably be best served if you start without gloves, so your reins don't get lost in your own hands. Once you feel you have a good grasp (pardon the pun!) of these rein positions, start moving from one rein position to the next without looking at the reins in your hand. When you've achieved success at that, watch the "bit" on your reinboard to see if you can move through each position while leaving the bit level and still.
If you commit to these exercises, you'll be teaching your hand the dexterity and acuity that is necessary to work with the reins when you have a real live horse on the other end. The depth and quality of the feedback that your brain gets from your hands will improve greatly. The result will be that moving the reins will be closer to second nature, and you'll have more attention to give to where and how you are driving your horse, rather than to how you are handling the reins.