I realize that it's impossible to simulate a combat situation. But I think that shooting at target practice is wildly different from shooting under duress when lives are on the line.
How can someone without military or law enforcement experience practice shooting in a stressful situation so they can be better prepared if the time comes?
Here are some options off the top of my head:
Drills are useful since your body will likely default to what it trained. There are a multitude of drills from a multitude of sources (thunder ranch, magpul dynamics, uspsa stages, etc.), however I assume this is what you mean by target practice.
Exercise can put your body under stress to give you some small indication of what you might face. Doing jumping jacks or push-ups (With your gun tabled or in a very secure holster) and the firing a string forces you to control your breathing and pulse, and if maintained long enough causes muscle fatigue i.e. loss of fine motor control.
Force-on-Force is used by many law enforcement and military organizations to train for combat. This is when two individuals or groups run training scenarios against one another using non-lethal devices ranging from paint balls to lasers. Gas blowback airsoft pistols are likely the most cost effective method of force on force training available to civilians. Many airsoft guns have controls that function identically to the real thing, and many firearms manufacturers contract with airsoft companies to produce training pistols. Fear of failure, and small doses of pain may provide you with some quasi-realistic training. You and colleagues can simulate scenarios that you might encounter in your AO. The failing points of this kind of training tend to be using cover that wouldn't stop bullets, reduced sensory input (noise and light), and no recoil control training. Remember to wear eye protection.
Join your local IDPA group. While not the same as being shot at, the time constraints and various scenarios can add some decent stress and will have you practicing drawing, firing from cover, tactical reloads and target/threat assessments. If you feel your not being tested well enough, take a run shortly before your event to get your heart and breathing rate up.
You need to have partners and setup realistic drills using something like air soft guns (should be a given not to use real firearms). Think of scenarios, setup a drill or the scenario, run through it and critique afterwards.
There's a common statement made often by trainers in this regard: under stress in the real deal, you will only be as good as 50% of your typical day in training.
Training and running drills distills the muscle-memory into your arms, fingers, legs, etc. This muscle memory is what will typically default to under stress. Keep in mind you lose all fine motor control when under serious stress. If you train regularly, expect your training results to be to get worse by a factor of 1/2 in the real deal (it's not a perfect science, this is just what is typically quoted). This means hand-palm size groupings will roughly double in size.
Knowing some of the above, you adjust how you train to fit those common rules and guidelines. When your training reaches a level where you are near perfect, then you start adding stress (in the ways mentioned in some of the other posts) to the training, and repeat until that level of training reaches a reasonable level of perfection as well.
There are quite a few shooting schools you can go to, that will do this. And over time, you will better your abilities with self-defense and weapons. Shooting is a perishable skill, so it's particularly important you maintain a level of ability consistently.
I know that the querent will probably never see this since this is a question migrated from a now-defunct Stack Exchange site, but if you live in a large city, there's a decent chance that you can find a facility that offers classes with scenarios for combat shooting. I know that they exist in the Pittsburgh area, where I currently reside. Ultimately, the best way to learn is by doing, and this provides a safe space to experiment and to practice. And, as with any martial art, the only way to be effective in combat is to practice in a combat situation.
One method espoused by a couple CrossFitting military folks is to elevate your heart rate through exercise and go shooting. They call it a "stress shoot" and use a modified version of CrossFit's Helen workout (Vimeo), which means several rounds of running, kettlebell swings, barbell push press (substituted for pull-ups), and target practice.
The point is to train or test one's ability to remain accurate while fatigued, with elevated heart rate.
Dude listen up no. 1 army vet here, for real its mine mine... first off keep a round in the chamber and safety it...when the time comes take your trigger finger from safely on the side of your weapon to unsafe then fire. You need a buddy for this one tho, move as a unit in one path finding cover as one soldier moves to next cover and fires then you follow and do the same. This gets you comfortable shooting live rounds in a team fast paced environment. Yell cover me and I've got you covered. Paint balling will supplement this. Full on door kicking room clear in and house to house movement, if in woods its usually more open so you spread out and low crawl to avoid detection. I would get a good squad formation manual too, or just ask me! Oh one more thing if you did how dare you flag your battle buddy, let weapon point at buddy, and watch out in prone position no dirty little barrels...shame on me:-)
