Dragons should purr.
Dragons should rub their faces against their loved ones/kobolds/consensual property/hoard-polycule-members to coat them in pheromones marking them as that dragon's territory.
Dragons should stretch their legs and bodies out in a single flowing arching motion, when they get up from a nap in the sun/near a volcanic heat source
Dragons should be easily tempted with food and toys that activate their ambush/pursuit predator instincts
And Dragons should "nya" involuntarily when people compliment them