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.
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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.
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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.
martialarts.stackexchange.com/users/435/Wayne In Yak
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.
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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.
martialarts.stackexchange.com/users/1780/Macaco Branco
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.
martialarts.stackexchange.com/users/347/Dave Liepmann
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?
How can I practice shooting for a combat situation?
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Options include:  Drills, since your body will likely default to what it is trained to do. Exercise  can put your body under stress to give you some small indication of what you might face. 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.   Join your  local   IDPA  group. You need to have partners and setup realistic drills using something like air soft guns (should be a given not to use real firearms). Training and running drills establishes muscle-memory in your arms, fingers, legs, etc. Some ways of  practicing shooting for combat are to join a local group, using trainig drills, exercise to control breathing, as well as  using airsoft pistols. 
Some ways of  practicing shooting for combat are to join a local group, using trainig drills and exercise to control breathing and using airsoft pistols. 