Fitting A Saddle:
Some tips for checking the fit on your horse:

Set the saddle on your horses back without a saddle pad, but with a clean cloth between the saddle and horse if working with a new saddle. The front of the saddle should rest two to three fingers back from the horse's shoulder blade. You don't want the saddle interfering with his shoulder rotation. If this seems back too far, look at where the girth would be, you should have about 3-5" behind the "elbow" to keep the girth from interfering or rubbing the back of the leg.

Once you've determined position, check the tree fit. The saddle should not "perch" on the horse yet you should be able to get about three-four fingers between the underside of the swells or pommel and the wither before tightening the girth/cincha. More space than that is not a good sign, but continue checking before ruling out the saddle. Before girthing, check with your hand all along the underside of the saddle on the horse's back to determine if there is contact along the entire panel (English saddles) or underside of the tree (Western Saddles). At this same time, before putting a pad under the saddle; try to rock the saddle by holding the cantle in one hand and the swells/pommel in the other. There should be very little up or down movement. Look also at the saddle to see if it looks level as opposed to high in back or high in front. Some styles of saddles will appear high in the back because the cantle is higher such as Dressage or Highback Western saddles, so do not be fooled by "looks"; but few if any saddles will appear high in the front.

If everything has looked well so far, take the saddle off and put a pad on top of the clean cloth, replace the saddle and tighten the cincha or girth up depending on the type of saddle.

As the cincha/girth tightens, the saddle may settle down to two to three fingers over the withers. This is not a bad sign, but watch that the back of the saddle does not "pop up" 3-4". Also, as you tighten the girth/cincha, watch your horse. Look for signs of irritation and discomfort. Tail swishing, ear pinning, biting the air, moving away from you can all be signs that the saddle is pinching the horse. If these occur, you might want to go back a step and look again at how the saddle is sitting on the horse. If all is going well, you should lunge the horse for about 5-10 minutes and watch the movement and attitude. Once the initial "freshness" wears off, the horse should move into frame, with the head at a comfortable level and rounding up into the saddle. A horse that travels high headed, with the back hollowed out under the saddle could be trying to let you know that this is not a comfortable saddle for him. Especially if the animal adds ear pinning and tail swishing opinions to the hollow movement.