I’ve said in the past and on numerous occasions that I don’t want to see stories about elves or stories where Cthulhu shows up. Even in a good story, when these sorts of elements are used and borrowed, they end up detracting from the story in my eyes.
If you’re not filing off the serial numbers of these things, it’s either because you’re lacking creativity and hoping to rely on established tropes or you’re hoping that by connecting your piece to those related tropes that you can elevate your writing on the merits of the reference. Or somewhere in between. There are shout-outs, yes, and these can be great – Shub Niggurath as the final boss of Quake or the hipster cultist shouting “Ia, Cthulhu!” before the fat Italian editor gets murdered in Foucault’s Pendulum were AWESOME. But if Quake had been a parade of named monsters from Lovecraft as opposed to horrors that FEEL Lovecraftian, or if Umberto Eco had peppered his book with lots of “LOL, Cthulhu, amirite?” it would’ve drastically reduced the effectiveness of the references.
But more than that, have some faith in your creativity! If you’re damnably insistent on writing elves, fine, but if you want to go the “our elves are different route”, which face it, everyone does these days, take a pinch of that creativity that makes your elves different and call them something besides elves. If nothing else, calling your elves something else, even calling them Morves or Velse will be an improvement, because people won’t look at it and say “oh, look, another elf story!”
And eldritch horror monsters? Why Cthulhu or one of the other big-name badguy’s from the Mythos canon, unless you’re trying to coast on the popularity of Cthulhu (and there are folks who will read anything Cthulhu, but that’s not the point)? Name your own big bad evil scary monster god. Sure, he can be Cthulhu, but if you call him something like Uhlthuc you can fool folks into thinking you’re some kinda original writer guy, or something!
Don’t use elves or Cthulhu as a crutch! Yeah, I know that Cthulhu is a cottage industry, but I can tell you right now that your stories will improve by at least %15 or your money back if your evil monster beyond the gates is Uhlthuc and your similar-but-different elves are ‘the Velse’.
(Note: If you submit a story using the names Uhlthuc and ‘the Velse’ and I accept them on merits of story, I reserve the right to withhold the per-word bonus on the first 2500 words; file those serial numbers off harder!)