It tends to take a few tries to get what I want. With super well-known characters, like Mario, I dont need to add anything else. With characters that are well-known, but the name by itself isnt enough, I add the game that they are from.

Link from Legend of Zelda
Cloud from Final Fantasy

And if they character is obscure, I try to add a description as well, before detailing the scene.

April ONeil from Ninja Turtles. April ONeil has shoulder-length red hair and wears a yellow jump suit with white boots.

Beyond that, I just try to be as detailed with the setting as I can, and then I end it with the style that I want the image to appear.

The image is realistic.
The image is drawn as a cartoon.
The image is drawn as an anime.

Sometimes it turns out great. Sometimes it turns out like crap, and I just dont post it.