These don't irritate me in and of themselves, the way that prophecies do. It's just that people get them wrong so much of the time.
1) Know the purposes of your weapons. Swords are not throwing weapons. Longbows are very powerful, but likewise need great strength to draw them. Pikes will slow a charge of horses. And so on. It's depressing how much common sense gets ignored for the sake of looking "cool," so that heroes in amateur fantasy will run around throwing their swords.
Bows are a special problem. You can't just keep them strung all the time, for example. You can't draw a longbow at all without lots of practice and lots of strength in your arms. The bowstring easily snaps inward and hits the archer on the inside of the arm, which would make a lot of people shooting a bow for the first time drop it. Practice in archery is necessary just as practice with a sword is.
Yet amateur fantasy remains full of people who can just pick up a bow and shoot arrows straight at the targets the first time, without any practice.
This is where it's a good idea to show your protagonists training- or, if you really want to skip that and get to the "good stuff," have older protagonists who could have reasonably trained themselves to a certain level of skill. No miracle teenagers, please.
And don't necessarily base it off stuff in the movies, either. The charge of the Rohirrim down the hill at the Orcs in TTT was magnificent, of course, but it was also completely wrong. The horses would have been speared to death. Pikemen who set themselves behind their pikes are about the only way to stop a cavalry charge. Such a suicidal charge might make a good model for something you want an idiot general to do in your story, but not just to pick up verbatim without some kind of excuse.
2) Know certain facts about horses. Diana Wynne Jones in The Tough Guide to Fantasyland remarks that horses in Fantasyland must certainly not be real animals, because they can keep going forever without stopping to rest, and they never seem to eat or shit. To keep it from looking as though your heroes are really riding mechanical animals, some tips:
a) Horses eat a lot, and can't graze forever without getting sick. Some mention of buying fodder for them would make a lot of stories more realistic.
b) Horses can't simply be left on their own when your heroes stop to camp. They have to be unsaddled, groomed, fed, given water- a herculean task in itself if your group isn't camped near a body of water- and hobbled or picketed in some way so they can't run away. Any group of heroes outside Fantasyland who treated their horses like many people in amateur fantasy do would wake up the next morning to find their horses wandered away and probably half-starved, since they can't eat with bits in their mouths.
c) It takes training, for both horse and rider, to respond without tack. If your people regularly ride around bareback, they still can't do it on unfamiliar horses. Horses broken to saddle and bridle respond to signals from the reins as well as the rider him- or herself, and would simply be confused by someone who tried to use legs alone.
d) All those people prancing around on stallions are being idiots. There's a reason stallions in the real world are very rarely ridden: they're simply too wild. Mares and geldings are much steadier and less likely to waste energy in prancing around wildly or trying to mate (unless the mares are in heat, of course).
e) Warhorses have to be trained, too. The chances that an untrained horse in battle would deliberately kick or bite an enemy- or, for that matter, go unpanicked by the sounds of battle and the smell of blood- are minuscule. Training horses takes time, and warhorses should be valuable in your world.
f) Over a short distance, humans can run faster than horses, but horses will catch you in the end. And the only thing that can realistically break a charge of cavalry is pikemen or the equivalent (see above). I've read several fantasy stories of people who outran horses over a mile or more, or broke a cavalry charge of trained warhorses just by shouting. Wrong.
3) People do not linger from fatal wounds just to make dramatic death speeches. Fatal wounds include wounds through the heart, groin, and throat most of the time. Even if someone got most of their throat cut through and somehow lived for a few minutes, he or she wouldn't be able to speak. Same thing with a heart wound; the shock would most likely be too great. Gut wounds will cause someone to linger, but again, the wounded person's mind is more likely to be on the pain than proverbs or reciting a moral lesson for your young hero.
4) Wounds through the heart are hard to achieve. The ribs are in the way. It can be done, certainly, but someone untrained and young in the middle of his first battle would do better to aim for throat or groin, and it's hard to imagine a lucky strike slipping through all the bones (though easy to imagine a blade catching on them). Cutting the femoral artery or throat will cause massive loss of blood and quick death, and it's much surer than the heart.
5) Similarly, it's not easy to hack off heads. It takes a lot of strength, and someone who tries is more likely to waste time cutting through a thick neck. Meanwhile, an enemy will come up and stab her.
Executions aren't always neat and clean, either. It's estimated that it took fifteen cuts to get off the head of Mary, Queen of Scots. If you want the enemy to suffer, this might be a good idea, but your young untrained hero who's never handled a blade before would be wildly unlikely to make a clean cut.
6) Death smells. Bodies left unburied in a battlefield, especially in the height of a summer, will start to stink. This can make people sick. Also, if they aren't buried deeply enough, they can contaminate water and make people sick. Mass graves or mass burnings- for which wood must be gathered, and a large pyre built- are much more likely than an individual grave for each hero.
Blood smells, and not good to anybody except possibly a vampire. If you strangle someone, they have a last bowel movement, and that will smell. Unless your point is to emphasize the brutality of war, it would not be a good idea to have your king go straight from the battlefield to the crowning. Trust me, he won't smell like a rose.
7) Don't make one army "good" and one army "evil." If you look at history, one conquering army is as likely as another to loot, burn, enslave, kill, and rape. Unless your hero somehow managed to conquer his kingdom with a hundred people- or fifty, even better- whom he could keep an eye on at all times, it would make no sense for the "evil" army to be the only one making the peasants wish they hadn't been born peasants. It's particularly silly to insist that everyone in the good army is a shining paragon of virtue if the hero has hired mercenaries. Mercenaries get paid, sure, but they're probably in there at least as much for whatever they can carry off in the battle- victims included.
The Battle Between Good and Evil somehow takes precedence over all these little things, even though it shouldn't.
