Shooting well starts by having a solid connection with the ground. The closer you get to Mother Earth, the better your shooting position will be. That's why prone is the most stable way to shoot, followed by sitting, kneeling and off-hand -- in that order.
When you need to shoot while standing, your footwork will make a huge difference in how accurate you are and how quickly you can get back on target.
The fighting stance -- demonstrated in this video -- will get you going in the right direction. It gives the shooter improved balance, mobility and downrange vision compared to the traditional off-hand posture where shooter is at an angle in relation to the target.