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!)
Cirsova 
Whatever you do, don’t do hee-haw meets lovecraftian horror. Squidbillies beat you to it.
“Commence the burning of the metal money!”
You want cthelves? Because this is how you get cthelves. Or maybe svartalfar…
Working on a svartalfar story now. Might be too much horror for you, but I’ll try to keep it action oriented.
Right on! If it helps, know that Howie Bentley’s “Where there is no Sanctuary” in issue 4 is the upper limits of the extremity to which I’ll go.
Even in Mythos terms, Cthulhu was a one-trick pony whose time had passed in the 1920s. Sure, there might be true believers who thought he might have another shot, but it’s just silly. Many of HPL’s entities are very underused, despite plenty of potential. Campbell’s “The Voice of the Beach” and Klein’s “The Events at Poroth Farm” are both incredibly effective “Mythos” stories without ever invoking the Mythos. The same can be said for “The Colour Out of Space.”
As for elves…they can be featured in a myriad of ways. Poul Anderson worked “elven/fairy”-type creatures into a large percentage of his SF. I’m thinking of FIRE TIME, THE AVATAR and “Queen of Air and Darkness”, but there are quite a few other examples. Moorcock’s Melniboneans, Eldren and Vadhagh are simply “incognito elves”. A big problem is that many, many people are drawing from the same ultimate source: Tolkien. While I think — as did Poul — that JRRT did a great job, those elves were the way they were in order to play a role in a specific universe. There are plenty of ways to spin the original source material from European legends and folklore.
For me, the best was the Horror in the Museum.
Scooby-Doo ending.
But the monster that had been so terrifying was just the dead body of a small, comparatively weak one, so if a guy wearing its skin was that scary, what other real horrifying monsters are there?
Funny thing is, we just dropped a Lovecraft issue, and I don’t think that ANY specific Lovecraftian monsters or Deities are specifically referenced, except for the Great Old Ones and some Deep Ones.