The key to accuracy, and having the ability to knock the stuffing out of the X-ring is "repeat-ability" I'm assuming that you are refering to competitive shooting, or at least you are leading up to it.
Repeat-ability. This means that you try to do every shot exactly the same. Natural point of aim, Body Alignment, Sight alignment and sight picture, the slow - steady squeeze of the trigger, doping the wind. All these actions and more come into play when you are shooting offhand.
I try not to move my feet once I've established my natural point of aim and body alignment - especially when shooting my slowfire string. That's 22 rounds in 20 minutes or less. After I fire a shot, I rest the butt of the weapon on the stool and scope the target while standing. Shuffling your feet destroys your original natural point of aim.
I try to grip the weapon in the same exact place. I 'look' the butt into the same exact place in my shoulder, and my 'off' hand contacts the forearm in the same place.
There is little bone support to be had in the offhand position, this is why it's such a difficult position to master. It isn't easy - but once mastered it's probably one of the least fatiguing of the shooting positions.
So as long as you heed Mr. Lombardi's advice, and get some personal pointers from a High-power shooter, you should get the hang of it in no time at all.
There is a saying in High-power shooting that dovetails with this nicely... You can win the match on the 200 Offhand - and then loose it at the 600! Keep them in the X-ring!