The only "rule" is "Don't trim off any excess harness material until you know it is really excess".
If shoulder rigs. per se, are completely new, there are odds and ends tips on things to watch and things to avoid.
The harness should be centered on the wearers back. It will try to slip toward the weight of the gun, and that is why an off-side belt tiedown is almost always mandatory. Some say they can balance a loaded rig without one. I have never found this to be the case.
The harness should be adjusted until the straps lie flat across the shoulders and back. Any wrinkle there will print, and is a dead giveaway.
The harness, at the place where the halves join at the back, should ride as low below the back of the neck as possible, and not put pressure on the lower neck vertebrae.
Gun positioning is a matter of choice, and depends a great deal on body shape. A Schwarzenegger shape leaves a lot of room for a holster to hide, and drapes cover material well. A Dom DeLouise shape leaves little room error. I'm "medium broomhandle" shape, and try to position a horizontal rig just to the left and a little below the shirt pocket (using a pocket T-shirt for a guide). I like for the gun to ride just a little "muzzle up", and the butt rides against the lower curve of the ends of my ribs. Under a tail-out button front sportshirt, this allows the use of the pockets for usual, mundane stuff that can help break the outline. I carry a J frame in the Guardian even with and just to the left of the pocket. I carry a tobacco pouch and pen in the pocket of the outside shirt, and checkbook in the T-shirt pocket. I leave the top three-four buttons open on the outer shirt. I'm 70, and can get away with things a younger, snappier dressing yuppie would shudder at. A penchant for "style" is not necessarily beneficial to packing. Choice of shirts is important. I've found several at Penneys and Wal Mart with a mesh shoulder panel inside. Not too easy to find, but they are there. These also pop up in the Cabelas catalog at times. This helps break up any outline of the harness or center connector.
The off-side tiedown position on the belt can be important, in keeping even but not excessive tension on that side of the rig. Getting that right goes a long way toward keeping wrinkles out of the back of the harness straps. It can be moved forward or back to brace against the side belt loops to hold it in position, and still leave room for an IWB, worn at 4:00, or so, if you want to go completely heeled. If it is against a belt loop, it won't move a great deal. If it is between two widely spaced loops as found on designer pants, it may be in trouble.
Thats about all I can scrape off the top of my head besides dandruff for now. The rule about not removing harness material is the only hard and fast one. There is so much trial and error in fitting the first shoulder rig that it sounds like an exercise in masochism, but otherwise you've either wasted + or - $150, set yourself up as a target. It gets easier with a second or third rig, which is more than most will ever own. I use five, but they were collected over many years. They do have a place. Not all the time, but they can be used more or less year-round, in almost any climate (the Ken Null polymer rigs go tropical very nicely) and they can, at times, make a second or even third gun viable. No, this is not a Bear Thread
