Here are a few ideas that I would try to work into my other post if I were to revise it:
I think for new players having linkboys and porters in a dungeon expedition is essential. One reason is that each additional body makes a player character less likely to be a target if deadly combat ensues. But more importantly, it allows player characters a glimpse of the deadliness of the game without having to die themselves. Hireling deaths are foreshadowing. So, if a hireling gets dripped on and turns to slime, players can learn from it without having to die.
I think it is important, though, to make sure that even hirelings deaths matter, or they won't have much impact on players. I strive to flesh out hirelings as much as possible without bogging down the game. This means giving them names, memorable traits, sometimes faces, and an oath to try and keep them from being abused. Hireling deaths should matter, even if not quite as much as a player character's.
In the post I linked to by Trollsmyth, he went into a lot more about the dramatic possibilities of non-death incapacitation. I should have gone more into that too, because I think it's absolutely true. Especially true if we're going to rely on stories emerging in our games. It makes for duller stories if characters are only ever fit as a fiddle or stone dead. Unconsciousness should be possible in the system. It is actually pretty rare in all of the D&D systems even if you consider magical sleep.
Because of this I think that a house rule that allows for unconsciousness is important. I've been using the rule that 0 hit points, or negative hit points equal to a character's level, is considered being unconscious. I don't remember where I first read about this rule, but Ian named it A Hero's Death. I was thinking about doing away with it for simplicity's sake and because I felt it was trying to soften death, when death is intentionally part of the system. Now I think I'll keep it.
Related to the idea of incapacitation is the idea that foes may give a defeated party quarter; spare their lives while taking them into captivity. I think a newer DM may be harried by all of the data they are having to track into making all combat simple, to-the-death affairs. Or they may make the mistake of only stocking an adventure area with voracious, mindless beasts. The traditional idea is that players need to learn when to run away, and that's true. The other side of the coin, though, is that monsters should run away sometimes too. I think that morale is an essential aspect of making combats feel more real. And what better way for players to learn that running away is an option than to see a foe utilize that option?
But there is even more, even with a foe that is near victory over a party. Not every foe wants the party dead. Maybe they need living sacrifices. Maybe they need food for their young and wish to keep the characters alive until each feeding. Maybe they want the characters as a bargaining chip. Maybe they just want the party to leave. Having more depth to why combats are happening and what results are possible can have a big impact on how deadly a game is.