How to hide Plot armor

Plot armor is a term for the idea that the main character(and sometimes others) can't die because that would end the story. However, the characters still get into difficult and dangerous situations, so the author needs to make them survive somehow. Unfortunately, this usually involves something called "deus ex machina", which is when something happens in the story without any sort of explanation, such as the hero getting rescued right in the nick of time.
Plot armor is necessary for most stories, but when it's that obvious, people tend to get bothered by that, so here's some ways to make your plot armor less obvious.
　
1. Don't put your characters in a situation if you can't see a logical way for them to get out of it alive.
　
Many authors put their characters in ridiculously dangerous situations, like locking them in a room with a nuclear bomb set to go off, guarding the room with giant, fire-breathing wolves, and putting the whole building on an island in the middle of the pacific ocean surrounded by starving sharks. Then they make up some half-baked explanation for how the hero survived because he managed to defuse the bomb with a mere second left before detonation, single-handedly fought off the wolves with only a screwdriver, and was miraculously rescued by a helicopter that conveniently just showed up despite never having been mentioned before. This is bad writing.
To avoid this, only put your plot-important characters in situations that you can think of a reasonable way to get them out of, like locking them in a room that has a window for them to climb out of, or poisoning them with a slow-acting poison that leaves plenty of time to find an antidote. Basically, if you can't think of a way someone could survive this in real life, you shouldn't put your characters in that situation in the first place.
　
2. Don't give your characters supernatural levels of luck.
　
Many stories, such as the How To Train Your Dragon books and Harry Potter, have their protagonists survive through a combination of extreme cleverness and irrationally high luck. For example, if the protagonist is fatally wounded, and their only hope is to take an experimental treatment that has a 99.999999999% chance of killing them, you know they'll take it and survive. Instead, don't let them get injured that badly, or if you must, time it so they have access to medical attention immediately after receiving the injuries and draw out their recovery. When your heroes survive tons of experiences of which each one should have killed them, it becomes obvious that the only thing keeping them alive is plot armor. To avoid this, make it so that they would have had a decent chance of surviving even if they didn't have plot armor. otherwise, don't put them in that situation.
　
3. Don't make your characters survive suicide missions unelss it's through their own cleverness.
　
This is shown many times in Stargate, where the main characters will go on "suicide" missions many times and survive each of them. It's even lampshaded(noticed by the characters themselves) in Atlantis, when Sheppard says(paraphrased), "I've been on tons of suicide missions before." They're called suicide missions for a reason: They will kill you. How many times did you hear of kamikaze fighters surviving their attacks? Exactly. (In case you didn't know, kamikaze fighters were Japanese pilots in world war II that crashed their planes into targets, killing themselves in the process.) But if you insist on this sort of thing(which you probably do, or you wouldn't be reading this article), make there be a decent chance of survival, and let your characters figure a way out themselves.
　
An example of this would be a character planting a bomb behind enemy lines and then figuring out a way to stay alive afterwards, such as setting the bomb on a timer and hiding it, then taking shelter in a place that's far enough away from the explosion to be unaffected, or maybe escaping by stealing a car and driving to safety. This is much more believable than the character surviving against all odds through sheer luck alone, as that rarely happens in real life.
　
4. If your characters are going to be rescued, hint at that ahead of time.
　
Here's the situation: Phil is trapped, his back against the wall, down to his last bullet fighting evil mutants. Suddenly, his allies break through the enemy line, gunning down the mutants right before they can kill Phil. If this rescue happens out of the blue, however, with no warning, it will seem like a cop-out. Instead, mention earlier in the story that Phil's friends are going to go on a mission in the same area as Phil at around the time he will need saving. This is known as foreshadowing. This way, it will show that you planned the rescue all along and make it seem plausible for it to happen just as Phil needs it the most.
　
5. Don't make your characters beat the clock at the last second.
　
This is shown in the classic "Defuse the bomb with 1 second left" cliche. It's a blatant example of unnatural amounts of luck, which, as i've said before, should be avoided. Instead, have your heroes finish whatever time-sensitive thing they need to accomplish maybe 20 seconds before they need to, or even a few minutes. No, it's not as dramatic, but everyone knows they'll survive anyway, so you might as well make it believable.

6. Don't make your villains incompetent.

Many works make their villains stupidly insist on killing the heroes themselves, giving the heroes a fair chance, or monologuing their evil plans so the hero has the information he needs to win(called "bond villain stupidity"), or giving the bad guys terrible aim(called "stormtrooper marksmanship") and constantly just barely miss the heroes so as to keep them alive. This should be avoided at all costs.
First off, the villain likely isn't going to have any specific vendetta against the heroes so as to insist on killing them himself, and even if he does, he's not going to give them chances to escape. No one who gets to a position of power high enough to have an entire army at their beck and call is going to give the heroes chances to escape unless it's absolutely necessary.

As for minions with atrociously bad aim, just scrap that altogether. If they can't hit what they're aiming at, they're not going to be recruited as soldiers. In fact, most untrained people would have better aim than stormtroopers, death eaters, or what have you. Instead, make your heroes never get in the line of fire at all, have something to block projectiles(like a shield or bullet-proof vest), or just never give the bad guys any reason to shoot at them in the first place(like pretending to be on their side from the beginning and only fighting them while undercover). Alternatively, you could have them get hit, but not fatally, such as being shot in the shoulder or foot. It will require some time to heal, but it will make it seem like they don't have plot armor, or that it's not very strong.
　
Plot armor is necessary for most works unless you want an "everyone can die" scenario, which requires more characters and more effort. But this is no reason to make it so blatant as to be boring, ridiculously implausible, and predictable. People enjoy stories more when they don't have to suspend disbelief as much, so making plot armor less obvious makes the story as a whole much more enjoyable.