In my experience, murder is always the best cause of death (or at least the most fun one) when killing off charries, although it doesn't always fit into every story.

Disease is usually my second choice, because it can happen to almost any charrie in almost any setting, although it usually takes at least a week of the charrie showing symptoms before they can reasonably die, even if you've got an especially fatal and fast acting disease, and for most diseases it would probably take at least a month, which doesn't always work when you want the death to be out-of-the-blue. It would be rather strange if the charrie showed symptoms for one day and then died the next.

Accidental ingestion of poison is also a good one, because theres a heck of a lot of poisonous things somebody could accidentally eat or get into their bloodstream somehow, and if it's a fatal poison without an antidote (root of water hemlock is a great one, cause it looks like a pretty lil flower and it's fairly common in North America and it isn't too hard to have it just sitting on a pot on a windowsill and have a charrie accidentally touch (or eat) the roots of the plant somehow) you could just have a charrie drop dead right then and there and nobody would be able to do anything. I mentioned water hemlock, I've used that at least three times, and I've also used belladonna (AKA deadly nightshade) and pufferfish poisoning in the past, and I once had a charrie die because they ate too many cherry pits, because your body converts some of the chemicals in cherry pits to cyanide (which, needless to say, kills you). I beleive if I remember correctly it takes 20-30 red or black cherry pits to be dangerous to humans, but I had them eat more than that to be safe. I think the charrie just really loved cherries, and one day they got sick of spitting out the pits so they just started eating them all, and they ended up eating two whole cartons of cherries with the pits.

Accidents in general are a pretty good option, but I'd try to avoid boring things like car accidents unless you're intentionally trying to give them a boring death. It isn't too difficult to come up with an intereseting accident (see: accidental ingestion of poinson).

Continuing the accidental-death ideas, here's one for if the story happens in Victorian times or someone is a fan of very old decor: Arsenical wallpaper. It was very common in the late 1800s, if I remember correctly, except whenever it got damp the green paint would release arsenic vapor into the air and people would be poisoned.

Of course, there's also falling, either of objects or of the person themselves, and so on. 

um - don't :)

or if you absolutely must, make it be that he risked his life to save someone.

Try an attempted murder! The villian sends somebody after the main character (or somebody else) to kill them! To be honest it's one of my favorite plot devices... Hmm, maybe I like things involving murder just a little too much. I've mentioned it three times on this thread... What can I say? Murder can be a solution to just about anything.

I... unfortunately do not. But! I do know that if you involve murders in it it's much more interesting!

I haven't really written flashbacks but if I did, I would use wording like 'they had said' or 'she had asked' instead of 'they said' or something. this works especially well if the rest of the story is in present tense, but past tense works too.

I would also try to skim over most details, and call attention to random, unimportant but noticable things. idk though, that's just what I'd do :)

I have some tips! 

1.) Okay, so contrary to what Darkvine said, I really wouldn’t recommend using “they had said” instead of “they said” — just because I find that makes your writing awkward and slows the pace (however, if the rest of your story is written in present-tense, go right ahead and use “they said” instead of “they say”). I get that this is a logical way to convey that it’s a flashback, but there are other ways to show it that don’t interfere with your writing. For instance, include the fact that it’s a flashback beneath the chapter number (“Chapter 7 / three weeks earlier” or “Chapter 12 / November 2013” or even directly in the chapter title if you’re the type to name your chapters). You can also just have a sentence or two transition that indirectly states that it’s a flashback in in the first few lines of your chapter if it fits with your writing style, like stating the character’s age as being younger. Another option is to use italics, which I don’t really like to use, but it’s a personal preference, so I’ll include it — though if you’re going to use italics, it would probably work best for shorter flashbacks, and it might get tedious if you’re writing flashbacks that span several chapters. So in your case, I’d use one of the first two options. Of course, there’s plenty of other ways, too.

2.) Okay, so this kind of depends on what type of third person narrator, but no matter the type there’s some way of conveying emotion, because in flashbacks the name of the game is EMOTION. If the flashback’s important enough to be included in the story, it’s gonna have some sort of strong emotional connection to the character. This is easiest with omniscient and limited third (deep penetration, but you could make light penetration work), but whatever you do make sure to convey some kind of emotion. I like what Darkvine said about bringing attention to random details — for instance, if you’re writing a character’s tragic backstory, describe how the character kept focusing on the color of the sky, or some other character’s hands, etc. I don’t think I’m making much sense here but whenever I come across that sort of stuff, I find it really really effective. 

3.) this kind of ties into the stuff above and really only would apply to limited third POV, but if the flashback is a memory, I’d describe it like it’s a memory. Some parts might be fuzzy, some parts might be in sharp focus. There might be a specific scent or object or moment that stand out to your character. You might even you the unreliable narrator route and have them remember something wrong/skip over important details, either because it was traumatic, because they were a small child and misunderstood the situation, because important details were kept from them at the time, or because they were, like, brainwashed or something. Obviously there’s so many different ways you can go with this, so it’s interesting to think about.

4.) if it isn’t working, cut it. This one’s pretty important, I think. If the flashback isn’t important enough, takes away from your story instead of adding to it, is boring, or slows down the pace, either rewrite it or get rid of it altogether. 

Um yeah so if you read through all that, i applaud you, because that was kind of long and probably didn’t make much sense. Feel free to completely disregard this, but I do think some of the things I said are interesting to think about :)

If your story is in past tense, I do think that it might be beneficial to start out with "They had said", but then just go on to "They weren't acting like they were making a decision that would change everything". Also, assuming your story has a narrator even though it's in third person and the rest of it is in the present tense (for instance, there's something like "Occipetal thought that so much was happening so quickly" and "Occipetal felt like they were riding a tidal wave of emotions", but the knowledge presented to the reader about stuff in Occipetal's head does not occur for the heads of other characters), you can load the flashback with emotion, such as "Now Occipetal cringed, knowing that they had made the worst decision of that school year, maybe even that decade, all those weeks ago."

and now here I am, having completely forgotten about them...