- Every weapon is loaded until you have cleared it yourself. By "clearing" I mean, of course, removing the magazine or clip (in the case of automatic or belt-fed weapons), and racking the bolt or slide to inspect the chamber for loaded rounds. If you are at a range, there is typically a barrel available where you can dry fire your weapon into to reset the action and be sure the weapon is "safe."
- If possible, wear eye and ear protection. The more dangerous malfunctions can be explosive in nature. You also wouldn't want hot brass to fly into your face if someone carelessly decided to discharge their weapon next to you.
- Never rest your finger on the trigger unless you are prepared to shoot, instead leave it extended just above the trigger guard. This is known as trigger discipline.
- Always point your weapon at the "low & ready" (toward the ground), never up. It's much faster to bring your weapon up than it is down, and putting it up can obstruct your view of the target just long enough for them to get a fix on you first. Furthermore, if there is an accidental discharge, it's safer to have the bullet go into the ground than fly into the air and come down God knows where.
- When shooting pistols, use the stance that is most comfortable to you. But if you are a tactical shooter, a modified Weaver stance would be your best bet. This is what Law Enforcement Officers and military operators use most often. Both hands support the weapon (better for steadying the weapon and absorbing recoil), and you are turned sideways to the target to present a smaller profile.
- If you intend to carry the weapon on you, whether concealed or not, make sure you shop around and try out a few different style holsters before deciding on the perfect one. The perfect holster should be the holster you are most comfortable with wearing for extended periods, and can quickly and safely retrieve your weapon in an instant. "Locking" holsters, like two- and three-point systems, are very effective if you are concerned about someone trying to wrestle your weapon out of the holster, but they are not foolproof and can be a little tricky to learn how to quickdraw from.
- Anything worth shooting is worth shooting twice. Learn the value of the double tap.
- Headshots are difficult. Moving headshots are even more difficult. Aim for the center mass (chest/upper body), but practice those headshots anyway, because they could be armored.
- Keep a mental tally of your shots so you know when you have to reload. In a combat situation, it would really suck if you exposed yourself to take a shot only to find out you're empty. Pistols are easier, obviously, since the slide will lock in the open position, but certain rifles can be less intuitive. If you are capable of obtaining tracer rounds, you can rig your combat loads so that toward the end of a magazine's life there's a tracer every second or third round to let you know how many shots you got left. Be careful with this method, as Murphy's law tells us tracers work both ways (i.e., by exposing your position). You're better off keeping a mental score if you got the concentration for it.
- Learn how to disassemble your weapon and clean it thoroughly. A well-maintained weapon is a happy, functioning weapon. Preventative maintenance reduces your risk of misfires and jams.
- If you are really into tactical shooting, practice shooting ambidextrous! This is especially helpful when shooting from cover. If you are right-handed, you present a smaller profile peeking around a left-hand corner. So to maintain the same sentiment of presenting a low target profile, practice shooting left-handed for those pesky right-hand corners.
- Familiarize yourself with as many firearms as you can. Although it is generally not a good idea to use your enemy's weapons or ammo (you don't know their condition, they could be boobytrapped, etc), should the need ever arise you will already know how to work the action on it and rock-and-roll. If you can get range time on 'em, the better.
Ok, that's all I can think of right now. Remember: as you train, so shall you fight.