I shoot offhand all the time, mostly flintlocks all year round, but we do have a Winter weekly milsurp 100-yard offhand informal match from NOV thru MARCH. I once shot a 4" witnessed 10-shot group offhand @ 100Y whilst using a vintage 1870/87 Italian Vetterli-Vitali, using open 'BB gun' sights firing the obscure 10.4x47R old black powdah cartridge (loaded with sized-down 44-Mag 240grn boolits over a charge of Alliant 2400).
Point is ... besides practice ... everything of the shot process culminates in front sight, front sight, front sight ... WHERE is that front sight at the break of the shot and through the follow through? Basic foundations of a good shot, e.g., BRASS for breathing and aiming, etc., also requires a good stance that correctly establishes your Natural Point of Aim (NPA). This is where the 'aim' is held by the bones/framework of your body and not by muscle. Any rifle shooter or azzhat can muscle a rifle to shoot 1 to 3 good or lucky shots, but to shoot a bragging worthy group of 10 or more shots takes good technique.
To establish your NPA:
Get in your stance, but always keep your front foot fixed - do not move it. Get on target and close your eyes through 1 breath cycle then hold the breath as normal. Open your eyes. Windage first - if off to Left or Right then move your back foot a tad to swing the barrel onto the target. Be honest here - if you cheat the process - you're only cheating yourself!
Elevation - If ‘high’ on a target (dry fire or checking your alignment without shooting) bring your rear foot closer to the front foot. But if the front sight is ‘low’ of the bullseye, spread your rear foot out wider; always in the same orientation/angle. That sounds the opposite of what you should do, but it works, so for elevation always if 'high' on the target, brong your feet together which makes you stand 'higher' or taller ... but whilst shooting, this drops the muzzle.