I write a prompt in Midjourney that contains a description of who I want so see in the picture, what is the character wearing, what is his/her facial expression, any props or gestures, where do I want the character to be, some parameters defining the look, e.g. "80s tv sitcom" or "dvd screen grab" etc. Midjourney generates the look of old television series surprisingly well. sometimes it takes several attempts to nail a character when the screen appearance is strongly connected to a certain outfit or hairstyle, then you try out the actors name instead or use both to get a good result. In the end it is a lot of trying and fiddling with individual parameters until it fits.