You can visit Illusion discord server and find general guide for making renders in HS1 help channels in pinned messages (same technique can be applied to HS2, it just contains overall information about photography tricks like how to frame your object in render, how to make it "pop up", what kind of lighting you can do and how to tweak overall look of your render with all the options in F5 menu).
Obviously you also need fair amount of experience and understanding how to light up your scenes (great lighting alone can turn mid render into something really good). If we're talking specifically about quality (not taking efficiency in account), then I would say that Eternum's ceiling isn't impossible to reach as some people think. Surely you won't get exactly the same result as it's tough to "copy" someone else's preset and settings, but you can still reach quite similar look (especially if you're willing to learn a bit about post-processing and improve some rough spots in HS with the help of Photoshop).