Aspiring writers are sometimes paralysed by the fear that they'll be using other people's ideas, words, stories, characters. It might be the simple desire to behave ethically, and a fear of outright plagiarism or even of being sued for breach of copyright. Or it might be a more internal sense that your writing will be inauthentic, second-hand, second-rate, if it has whispers of someone else's work in among your lines.
It's an understandable worry, not least because our Western tradition of art lays such stress on originality. And yes, outright plagiarism does matter ethically, as breach of copyright matters legally (though I'm always surprised by how many writers don't understand the difference). But in fact there's nothing new under the sun, and I honestly, genuinely would advise you not to worry about it. All writers were readers first, and all books are rooted in other books, and there are only seven basic plots anyway. There are streaks of my favourite characters and situations in all my work - there's even the occasional hommage, as I talked about here - but I doubt if anyone else would see it except me.
I can't remember who said, "Bad writers copy, good writers steal," [18/12/13: it was Picasso, says Caroline Lawrence] but it's true: what matters isn't where stuff comes from, but which stuff you pick, and what you do with it. If you lift two characters straight from another book, complete with their stories, their voices, her taste in whisky and his taste in lapdogs, then most readers will sense the inauthenticity of them in your story. They didn't grow in, and out of, your imagination and consciousness, but from another writer's consciousness, and we'll sense it. The same is true if you raid, say, the setting and structure of your story straight from a successful TV series, rather than going to the original places and drawing out new stories from a real firestation or housing estate. We'll feel that it's second-hand: that it's a copy - a cardboard copy - of the real thing, and we'll sense the struts propping it up. The contract is broken, because you're not dealing "honestly and justly" with your readers, as John Gardener puts it, and in return - or, rather, in retaliation - your readers will no longer "agree to forget" that this story never actually happened.
Yes, all humans have the same skeleton, but even the nation's dukes are very different from each other, and so are the newsreaders and the footballers. That's not to say you need shy away from the basics of the genre you're working in. A country house mystery set in the 30s probably does have a butler, who will be a man, and not unlike the narrator of The Remains of the Day in several important ways. A detective story set in modern Glasgow will have some police officers in it, and quite a lot of the time they'll behave in ways that we would expect, or, at least, ways which wouldn't surprise us or the writers of Taggart. Everyone does conform to many of the stereotypes of their job, age, gender and so on.
But beyond that basic sense that your characters need to have skeletons which are believable in that basic, simple sense, it's up to you. It's you making the skeleton dance and one of the things that makes your characters believable is, exactly, that they're not second-hand: there are things about them which we've never met before, because you've imagined them. As I was exploring here, second-hand things slide over and off the mind without the reader really experiencing them. It's the rough paint of newness and (perhaps small) surprisingness that catches the eye, and it's that which makes our experience of the character seem alive and immediate. (That's why, for example, I reversed the stereotypes of her lapdog and his whisky, further up.) You'll have stolen these characters, in other words, only in the sense that a bird steals twigs from a plant. You make those twigs your own, by weaving them into a nest.