While there is no “one” (or eight) trait that guarantee a person is smarter than average, studies have indicated that highly intelligent people do share certain traits.
I do want to make a point about the recreational drug usage. This chart and these studies are NOT advocating the use of recreational drugs. They’re suggesting that people with a high IQ in childhood may be more inclined to seek out “adoption of harmful behaviors” in adulthood. So don’t go stock up on crack, folks!
Also, here is a ginormous list of books that will make you smarter.
Go in-depth on the data here: 9 Science-backed signs you’re smarter than average