I shoot the off-hand the way I was taught in the Marine Corps...
Tight sling, feet perpindicular to the target, slight lean back, (right handed shooter) left elbow cocked out to keep the sling tight, right elbow dropped close to the body and on the hip bone if you can reach it without muscling up, good firm cheek-weld, high firm pistol grip, controlled breathing, and interrupted trigger control.
In the 10 years I was in the Corps, I never dropped a single round on the 200 yd line in the off-hand.
The last year I had to go to the range, they were instituting new off-hand rules to teach how to shoot with the new body armor that I absolutely despised and felt awkward... but they worked as well. Before the new armor with SAPI plates, they taught us to stand sideways to provide a narrower target to the enemy... after the SAPI's, they taught us to stand facing the target to give the enemy the SAPI plate shot.
Expert USMC Rifleman (x5)
Sharpshooter Pistol (sorry guys I hate the M9)
Novice Re-loader (tips are welcome anytime)