O.k., so we are have been transported into our favorite post-apocalyptic scenario. Where you are, and what means you have at hand are generally rather limited. It seems like only the bad guys can get hold of an armored brigade, or in a pinch a light recon unit. Bad guys also don't have fueling problems. When the good guys are prepared, they often are on some visit far away from home, and have to travel great dangerous distances. In our fictional settings the men usually meet Calypso somewhere along the lines. Not a deadly threat but you might want to familiarize yourself with some Vanessa L. Williams trivia, so you will have something to talk about: don't bring up that old pageant deal.
We will start of with a basic scenario. We are a the characters trying to defend our little collection of homes. We will also presume you have some sort of motley collection of people with you, so our conversation doesn't de-evolve into a point-and-shoot discussion. What would you really do?
Well this only Part 1 (of 7) so we don't have to cover all the ground here. what works, often sounds easy.
The problem is knowing what is working. Combat, at all levels, is confusing. It is both terrifying and confusing when the bullets are flying around your vicinity.
In modern combat, or even very early skirmish type wars (American frontier) you often did not get a very clear look at your enemies. Where you facing 12 men or 120? Did you shot 50 of them or five? These don't seem like insurmountable problems, but where reported numbers can be cross checked with later documentation, the track record for self-reporting accuracy is very poor.
Combat Effectiveness: Cohesion, Stress, and the Military Volunteer Military
Sam C. Sarkesian, Editor, Sage Publications, London, 1980.
It is natural enough that people maximize the likelihood of doing what they want to do and that in which they feel proficient. In World War 1, British destroyer captains resisted convoy duty - as did their Japanese counter parts in world War 2 - hungering for general fleet actions which rarely came. In a related vein, in 1942, and analysis of post strike photos was distributed to Royal Air Bomber Command Group commanders. The report concluded that 10% of the bombs dropped landed within five miles of their targets. Previous estimates indicated that the bombs were landing within five-hundred yards of the target. One group commander scrawled "I will not accept this report: across the file. In such cases, then, the spirit of a band of brothers at the micro-level drifts out of phase with the purposes of the macro-system.
Such perceptual filtering is also evident in the differences between claims of 5.7 million tons sunk in 1944 by U.S. submarine forces in the Pacific and the postwar kill-credit of 2.7 million tons computed from examination of the Japanese records and other data. A similar misperception occurred when the British claimed over 180 German planes shot down on August 15th, 1940 Postwar research showed that only one-third that number  were destroyed...p33.
So people are often highly mistaken in how effective their efforts are in combating the enemy. In most cases they do not inflict as many casualties as they think they will. As we have noted earlier, outside of a tiny fraction (around 2 to 3%) their shooting is an order of a magnitude worse than the results they get at the rifle range. If a group is attacking (3 to 1 odds) your collection of homes, normal results is for there to about one-half a casualty for every person defending the place: so if you have a dozen rifles defending the place, the 36 attackers would experience casualties. That is not what fiction tells us. Your usual fiction story has even the least competent defender, usually the young son, causing at least one casualty by themselves.
You will also become greatly confused and disorientated. Without the sophisticated communications system of the most modern armies, it is very easy to start shooting at each other by accident. Take this example from an experience in the former Yugoslavia when the lead started flying.
The setup begins with a friend telling me how he was injured.
Real Survival Exercises
Selco, SHTF School, 24 June 2012
They hold position in one of the ruined houses on far outskirts of city, more like a small settlement a bit outside of city, he was there with 12 more guys when attack came.
He says attack was so great that they fired few rounds only in response and then started to run, in very loud situation, with lot of firing and explosions they had enough time for very short discussion and plan, so they agreed that they run and retreat to a position some 2 miles from that house, if things get rougher they agree that backup position would be 1 more miles from first one.
The firing continuous. One of them is shot in the head, and they have no time to stop and look after him. When they get to the first rally point the lead is still flying. They don't slow up, they keep running. They come to a woody area, it is dark outside and in the woods it is pitch black. Bullets are still flying.They split in groups of 3 people and start to run trough ruined settlement.
"did you ever run through woods, in pitch dark, while bunch of the guys trying to shoot you?“ ..
On some small clearing he gets bullet in the thigh, and fell down, other guy helped him, while they keep running and he dragged himself through the woods, they start to use hand grenades in the direction where they thought attackers are coming.
Anyway they threw lot of that stuff, and after some time, everything went quiet.
O.k. So they have made their escape. Eventually 4 more people show up, two of them wounded. So 3/4ths of them are casualties (wounded or killed). Sounds very straightforward, overwhelming attack, lead to a precipitous retreat. The defenders, presuming they were heavily outnumbered might have inflicted as many as 12 casualties themselves. But it is not that simple. The tale continues with the last arrivals telling their tale:
Those two of them tell them that they get wounded with hand grenades that someone was throwing on them in whole confusion and dark.
They said that probably other guys from the group get killed on same area in the woods, maybe from the same grenades.
So yes, in the panic and confusion, they were fighting each other. A large percentage of their casualties (at least 2 of the 9) were from friendly fire (grenades).
Reading the account of this little retreat is a lot scarier than most of the apocalyptic fiction you will read.
As John Keegan noted (from first reference), in The Face of Battle, when he suggested that the "darkest fear of every commander is that the latent crowd within his army should by set loose by panic or defeat".
So our first points of order: be realistic, and don't panic.