Lets give Bob a red shirt, see what happens
More seriously, it depends on the character. If I’ve grown attached, I will typically procrastinate in the story, making sure they’ve had a good time, before I do the deed. Method, the method, unfortunately, more depends on what I’m trying to achieve, and i generally go for simple methods too. (Shove in front a train is about the most complicated I’ll do; gunshots are relatively humane.) There was one character I took out last year, and the location was a nice suggestion from @DirtyAngel.
In my current series, I tend not to depict on-screen deaths too often, I will but not often, instead typically making it out-of-sight, so it’s more of, ‘look, there’s a body!’
And while committing the deed, I’ll adjust the soundtrack on my computer, typically more sad/sorrow that helps me put me into that right frame of mind to follow through with it.
My $0.02 worth.