During my years as a game master I have used different techniques when performing different characters. I\‘ll describe one of my techniques here and perhaps you will describe one of yours?
minor npcs: (The duke\‘s chef, the village smith, etc…)
Clothing: I use the same tones of colour on the character\‘s clothes -I began doing so after I discovered many players have a hard time remembering a person, especially if the npc is too complicated.
In addition I try to convey a certain feeling; \“poor\”, \“obnoxious, \“foppish\”, \“flirty\”, etc. through the clothing (and of course through their personality).
Face and body: I use the same technique here. i.e. Beggars got long, crooked noses and rotten teeth, while wealthy merchants are fat, with make-up and oiled hair. For minor characters, stereotypes are good.
Personality: It is important to have just one, or at least very few, flavours to the personality. If minor characters are portrayed in a complex way, most players won\‘t remember. The personality should be exaggerated slightly to make an impression with the players.
Area of effect: This is the influence the personality has. A sadistic innkeepers area of effect would be the barmaids and the unpaying customers. Most minor npcs won\‘t have a large area of effect. A beat up barmaid, crying in the gutters will be a good hint at the innkeepers true self.
Voice acting: As I am a 6\‘8 tall man with some 260 lbs of weight, I have a deep voice. I realize that frail, elderly ladies are beyond me, but still I try to voice act as much as possible. Voice acting is a great way to further emphasize the personality of the npc!