Get a air rifle and pistol for quiet marksmanship training even indoors, look for airguns that handle and feel like your real weapons. Paintball guns and safety masks will let you practice defensive and team combat indoors and out, remember paintballs stain and break stuff, so talk to your squat mates before planning indoor combat. Airsoft (or soft-air) guns have several advantages over paintballs for use in close range training: cheap ammunition (1000s rounds for $5-$15), less damaging to walls/glass/skin, and there are many types of soft-air guns available (pistols, rifles, shotguns, etc.) Paintball guns are more effective for training outside, at ranges up to about 40-50m. Beyond that it becomes unrealistic. Think: a paintball takes one second to travel 90 meters, I rifle round will do that in .10-.30 seconds. there's an obvious inconsistency here.
If you can find a summer or winter biathlon competition or trainer you will learn the difficult skill of shooting while winded, which is typical of most combat.
You can develop a steady aim by putting a heavy weight on the end of a broom stick and holding it like a rifle, or by holding a weight out with your hands shaped like a pistol. Do this for several minutes a day and you will soon have no problem keeping a steady aim.
Owning a gun ain't shit unless you know how to use it. They make a hell of a racket when fired so you just can't work out in your den or cellar except with a BB gun, which is good in between real practice sessions. Find a buddy who served in the military or is into hunting or target-shooting and ask him to teach you the fundamentals of gun handling and safety. If you're over 18, you can practice on one of your local firing ranges. Look them up in the Yellow Pages, call and see if they offer instructions. They are usually pretty cheap to use. In an hour, you can learn the basics you need to know about guns and the rest is mostly practice, practice, just like in the westerns. Contact the National Rifle Association, Washington D.C. and ask for information on forming a gun club. If you can, you are entitled to great discounts, have no trouble using ranges and get excellent info on all matters relating to weapons.
A secluded place in the country outside city limits, makes an ideal range for practicing. Shoot at positioned targets. A good idea is to blow up balloons and attach them to pieces or boxes. Position yourself downstream alongside a running brook. A partner can go upstream and release the balloons into the water. As they rush downstream, they simulate an attacker charging you and make excellent moving targets. Watch out for ricocheting bullets. Have any bystander stand by behind you. A clothesline with a pulley attachment can be rigged up to also allow practice with a moving target.