While this is the way I personally would harness a horse, I am sure others will hopefully share how they harness up.
The following is part of an article I found, on harnessing a horse, writen by Bill Morong, and dedicated to "trying to help modern drivers and their horses enjoy driving safely and comfortably."
It is a very good article and hopefully you will take the time to read the entire article, here is a link. This is also a very nice harness shop.
Camptown Harness - camptownharness.com and horseharness.com - 800-717-0957
Starting with the first piece of harness I put on.
The Breast Collar:
The horse accelerates the vehicle by pushing into a collar, through which force is transmitted through traces to the vehicle. The collar distributes the force of draught over a suitable portion of the horse's musculature. Two kinds of collars are used: hame (or neck) collars and breast collars. Breastcollars are usual, except for the most formal turnouts and for heavy draught work. The breastcollar comprises a wide strap encircling the breast of the horse. It may be fitted with large buckles at its ends, into which the traces are attached. Sometimes traces are sewn on, which limits adjustment and makes unharnessing in an emergency more difficult, unless suitable provision is made at the rear of the traces. If a breastcollar is used, more sawing motion will be transmitted to the traces than with a hame or neck collar. Therefore, with a breastcollar it is imperative that the vehicle be equipped with a pivoted singletree to facilitate this motion, or the horse may be sored. The breastcollar should be long enough so that its buckles are not riding on any part of the shoulder, but must be short enough to avoid interference with the saddle and shaft tugs, allowing for the movement of the horse. About two inches on each side between the foremost part of the saddle and the extreme tip of the breastcollar is< usually good.
The breastcollar is also fitted with uptugs with buckles, which receive the billets of the neckstrap. The uptugs are subjected to much movement from the horse's action. They are weak points in the harness and should be examined for wear, pulling out of the breastcollar, and bent buckle tongues when harnessing up. The neck strap supports the breastcollar, the height of which controls the point of draught. The point of draught is the center, in the vertical direction, of the draught force. The point of draught should be low enough to avoid interfering with the windpipe, but not lower, lest the action of the arms be hindered.
Neckstraps can be made with single or forked billets. Forked neckstraps are best on horses with low action, but tend to make the breastcollar rock from branch to branch on horses with high action, which is most unsightly. A forked neckstrap is most useful with Fjords to move rearwards the point of support to minimize crushingof the mane. The neckstrap is usually fitted with neck terrets, through which the reins pass, to avoid atching the reins under the shaft tips. The neck terrets often introduce a bend in the line of the reins, which may interfere with the communication between the hands and the bit. To avoid this interference either use no neck terrets or adjustable-height neck terrets.
Photos of a breast collar with buckle in traces and showing the uptugs, and a two forked neckstrap, with terrets.