There are a few general rules of thumb that you can use in any state/city that allows for firearms to be carried and used for self-defense:
1. Don't draw your gun unless you plan on using it. Along with it being rather stupid to carelessly wave a weapon around in the first place, you can clear yourself of a lot of legal gray area if you only pull the gun when the situation has devolved to where you would not be escalating the conflict by bringing a deadly weapon into it. A major part of the controversy around Zimmerman's actions was that it's difficult to justify (even in Florida, which is a very free state when it comes to guns) pulling a gun and shooting an unarmed attacker. Of course, he had a whole mess of stupid decisions beyond just choosing to shoot someone who was punching him in the face, but that's a very important thing to remember: don't pull a gun out unless you're prepared to kill (not injure, kill) the person in front of you.
2. If it's a situation where you have a gun but don't want to just pull it out and start screaming and blasting away, loudly and plainly inform the guy who's acting threateningly that you have a gun and you're not afraid to use it. If you're in an empty parking lot and someone continues approaching you after you tell them to back off AND after you tell them that you're armed, you can probably guess that they're up to no good. Probably the kind of "no good" that means that they're not afraid of getting shot. Maybe because they plan on keeping you from shooting them in the first place.
3. Never "shoot to wound." Ballistics is an inexact science, and guns tend to do weird things when they hit people. There was a case a while back of a man who was shot at point blank range by a cop with a .40 S&W handgun and the bullets, for literally no verifiable reason, stopped barely an inch into his body without expanding. Likewise, Ronald Reagan's attempted assassination was done with a .22 pistol and several people (including Reagan) very nearly died from a single bullet and Brady was infamously left permanently crippled and trying to keep people from getting their hands on guns for the rest of his life. "Shooting to wound" is almost impossible; even a shot to the leg or arm can tear up blood vessels and result in someone bleeding to death before they can be saved by paramedics, especially somewhere where emergency services can't show up in 2 minutes or less. Going hand in hand with #1, you don't use a gun unless you're ready to take a life.
In the case of the Florida woman, I'd definitely argue that she could have reasonably believed that her life was in danger. But you actually don't want to fire "warning shots" for a few reasons: along with trying to use a deadly weapon against someone without killing them (which, again, you really shouldn't try to do), firing a gun in any direction except at the target means that there's now a bullet flying somewhere that it shouldn't be flying. Even .22 rifles can send a bullet traveling with potentially lethal energy for a mile, to say nothing of virtually every other gun that has higher power.
That's one of the reasons I hated Biden's spiel about home defense with shotguns, where he talks about firing shots into the air to scare the burglars/attackers away and even something as stupid as shooting through a door or wall at the target. If you fire both barrels of your shotgun into the air, not only are you now holding an empty gun against people who may want to kill you (especially since you just showed up with a shotgun), but there's quite a few pellets flying through the air ready to land who-knows-where. Potentially on a neighbor's car. Or a neighbor.
