A sling can give comparable stability to a bipod and allows much greater flexibility in stance, standing, kneeeling, sitting, prone etc.
The "chicken wing" stance with the weak hand supporting the stock, wrapped through the sling as noted above will steady you noticeably.
However that is only the first and to a degree least portion for accuracy
Next issue is breathing control, this can make the difference between and X ring and a flyer.....
Bring the rifle snugly to shoulder (if it's loose it'll hurt)
Don't do a death grip on the grip or stock as you will shortly start to micro tremble as your muscles tighten up.
Sight and breath in and out normally, do not take up tension in your arms.
There will be sight wobble, mostly be vertical at this point and is a natural consequence of breathing......quite important to you....
When you have the target acquired, take any slack in the sling up and breath in and out deeply twice, FULLY. Expect the rifle to move up and down in a vertical plane.
On the second breath out, exhale, stop and do not "hold your breath", you have already flushed the carbon dioxide, which triggers the breathing reflex and you will not feel a need to breath for 5 -10 seconds.
Vertical wobble will be minimal now, bring the sights down to the target and squeeze the trigger, following through and then safety on and relax.
If you still don't feel you are sighted well, want to shift position etc stop, finger off trigger, safety on, tension off hands and arms, wait a short time and restart the process.
If you stay in tension or hold your breath you will quickly start feeling your lungs and blood flow pulsing and you'll be all over the target.
The idea is to surprise yourself when the round goes down range.
You can do a lot of this at home before going to the range so you are prepared before hand.
The biggest points are be comfortable in a position, know your limitations and enjoy what your doing. The more you fret the worse it'll get.......