If you haven't cottoned onto it already, the past three entries have been stressing that if you're going to kill off a character, do it for a reason, a good reason at that, and then work on how you're going to present that. Red-Leather-Alert is a term I use whenever I see that something has gone terribly wrong in the translation between me writing something and somebody reading it. The last case I had was where one of my friends read a scene thinking one of my characters was confessing that they were, quote, "very gay", when actually he was talking about his own brother...(not good - suffice to say that scene has been reworded quite a lot!)
So you've decided you want to kill off a character. The next step is figuring out how (there's a long list of ways to die, and in literature it gets even more unorthodox.) When it comes down to the effect on a reader, pace is key. Kill a character off too fast (say, an explosion) and not allude to it enough, a reader might even wonder if a character is dead or not. Done successfully, it would give a reader a serious case of gape-jaw. Usually, a quick kill is done to stress action over emotion, and a slow death, perhaps from a fatal wound or a disease, lets you be heavy on description and really work on pathos. Of course, drag it on too long and a reader might even get bored and, say I say it, skip a paragraph or two - RLA.
As a reader, the worst thing that I can experience is the death of a beloved character done in such a way that I begin to stop caring. Let's say I've had a feeling that character was going to die for a while - perhaps the way they've been talking for the past few chapters has been rather consummated, or the main character has frequently mentioned how much they love this character and how they couldn't bear to lose them. So it's a nightmare for me when, after thinking of such a heartbreaking scene, I'm presented with one that's pretty naff.
I'm going to use one of my favourite examples of a book (my opinion of course) in which I was left with this "I don't care that they're dead" feeling. Mockingjay by Susanne Collins (I apologise to those who thought it was a good ending, but I'm going to give my thoughts anyway.) This third and final book to The Hunger Games was one that I very much looked forward to, and entered into reading it with enthusiasm, but the knowledge that bad stuff was going to go down. It didn't disappoint, a lot of people died, but I shut the book reflecting on those deaths, and all I could say was "oh." Now, perhaps its me, though I don't think I'm an emotionally blighted reader. All I know is that the deaths that others talked out as horrible where they were balling their eyes out, didn't thrill me very much at all. Of course, Mockingjay is fast-paced with a lot happening at once, but in the process of this, I began to feel as if this was an excuse for neglecting the death of some beloved characters. I do consider that this might be Collins' aim, to show that people are dying left, right and centre and Katniss, as our one source to elicit emotion through, can't falter.
But of course I have to compare to other fast-paced events where I was balling my eyes out and practically screaming at a character "no! Don't you dare! Don't you dare die on me!" (I say, again, Red damn Wedding.) The worst feeling I can have when reading is the feeling that the author rushed a character's death and therefore didn't give their own character the dignity they deserve. Sadly, this was the sort of feeling I had shutting Mockingjay. I don't think anybody who loves books, reading or writing, can say that a character is just a character. A writer gives them a spark of life, and the reader flexes their limbs for them. In the same way that we expect ourselves to be respected in death, so I feel our characters should be. As demonstrated, there must be a reason for a death, even if maybe we aren't fully conscious of it and it's just that "feeling" that I tend to have. Every character, and I mean every single one, is the keystone to a plot arc or an event in one way or another, and in the same way that an architect values that piece when placing it, he should take equal care in removing it, with full knowledge and justification of the structure crumbling down and becoming dust.