Caveat: I don't write.
I do, however, master and play Tabletop RPGs, so I have designed and played in a few fantasy settings along the years.
Tolkien races are a good starting point, because they're easily recognized by anyone, meaning you're not going to lose your newcomer. Of course, unless you actually want to play in Middle Earth, you're not going to have the exact same setting, so your elves will be a little different.
And that's actually a good way to introduce your version of elves: "oh, yeah, we've got elves in this world, still tall and eary, loves a longbow, but they're different from Tolkien elves on this and that point". It provides context, and allows you to have both familiarity and originality, in a fairly low time.
Same goes for space opera. You want to give your players a sense of the tech? Just compare it to Star Wars already, point the difference, and everyone shares the same universe!
My point is that benchmarking yourself to a widely known reference is a fast and efficient way to share the specificities of your setting. It will work when you communicate outside of the setting itself, like online forums or pre game night discussions, but the descriptions still need to be woven into the story.
That being said, if you want to describe your elves as small, girthy, beardy beings who love forging and beer, just to be different, you can skip the trouble and call them dwarves already, and everyone will know what you're talking about.