Steve - pretty much as you do with the arms straight when shooting a single shot ML pistol, but left hand grips the right hand, squeezing the right hand onto the grip. I sight down over my right armThe right hand merely squeezes the trigger straight back to fire the gun. In itself, the right hand does not grip the pistol with it's fingers. I have shot with left arm bent at the elbow, tricept resting on my pectoral muscle - I change back and forth, depending on how my back feels. Neither postition seems to hold better accuracy than the other. With an accurate pistol, like Taylor's .60 Hawken Pistol, I've easily shot 50's at 25 yards, as-has he, all balls in a 2" circle (outside diam).
Gripping with the right hand, is what usually pulls shots right and low, due to squeezing the hand more tightly as the trigger is pulled - called 'gripping'. Much depends on the amount of pressure the trigger pulls. Increasing the grip (tension) with the left hand while squeezing, can pull the shots left and low. Heeling, pushing with the heels of the hand sends shots up, as-will showing too much sight. Flinching with a long barreled handgun can throw shots all over, but usually low- sometimes right as with a rifle.
I stand with feel shoulder width apart (mine are quite wide), legs locked at the knees and shoulders square to the target, leaning slightly back - again, depending on how my back feels.
The above is for deliberate target shooting with the single shot handgun.
If someone wanted help, I'd have them shoot this way. If they insisted on shooting or wanted to shoot sideways like on TV, I'd let them as long as they were safely doing it.