I think everyone's Hyperborea will vary a little bit, emphasizing some aspects of the setting over others. I tend to run my games during colder, darker years, for example. With that caveat, when I introduce the setting at a convention game, what I say has evolved into something like...
"Thanks for signing up for Astonishing Swordsmen & Sorcerers of Hyperborea, which takes place in Hyperborea, a setting inspired by REH, HPL, CAS, Leiber, Moorcock, Vance and others.
Hyperborea exists as a chunk of icy, mountainous land, ripped away from ancient Earth's surface and spinning through the void while its surrounding sea spills into infinity. A bloated, dying sun skirts the horizon, never fully setting or rising. Saturn and its rings loom in the red sky, while two moons rise and fall. A great plague wiped out almost everything 1,000 years ago and the surviving Amazons, Atlanteans, Hyperboreans, Kimmerians and Vikings, among other mythical people, never really recovered, leaving plenty of ruins to explore, though filled with alien, demonic, twisted, mutated and elder things, all hateful and hungry. At best, the gods are uncaring, and at worst, they're vengeful, so steel, sorcery and ancient technology like radium pistols offer the most reliable aid!"
It's not perfect, but I try to differentiate it from something like Greyhawk or Tolkien (both of which I love). I add more specifics if people have questions and as the game situation warrants. I also try to drop in basic setting flavor here and there, like:
- It's cold and snowing now, so you are happy to have warm sabretooth furs.
- There's only four hours of light these days, from 10AM-2PM, and it's only the dying sun's sickly red rays.
- The last time you saw other people was three weeks ago, when some priests of a Thaumagorgan death cult wanted to trade a few diseased slaves for steel and wine.
- You can see Saturn and Hyperborea's two moons in the sky tonight, which bodes well for tomorrow's travel.
- A herd of mammoths appears on the horizon, thundering in the distance.
- You see a small patch of dangerous lotus plants, just off the trail, and a few red deer, rotting near them.
Again, that's how I do it for my games. Your game might happen mainly during lighter, warmer years. Hope that helps!