Describe the first time the PCs meet one / some.
Names after a few encounters or if they ask a loremaster "what is it?"
By the time my Tiamat group went after the Green Wyrmspeaker, I would say "about two dozen kobolds", everybody would look at the Wizard and say "Fireball" - because we all knew Kobolds didn't have the HP to survive that.
Nobody has actually sat at a table I DM'ed with a Monster Manual in their lap, trying to figure out names from my descriptions. Probably because they saw me trying to do same as a player and just failing.