They use adjectives to describe the characteristics of their character, and when using dialogue they'll sometimes have them use witty remarks or have them be more bland based on the personality that hey wish to convey. Also, an author will, after or before dialogue, add an adjective to what they're saying. For example: "I've been there before" Victor, said casually. Or: Ashley yelled "Well you should have known!" punctuation is also a key element in conveying a character well.