Bonus points if the author first mentions a specific trait, physical build, or whatever else halfway through the novel and totally fucks up my mental image.
I don’t expect a biology model description for each character, but write me something brief and evocative of how they should look, you fucking dork author. I don’t even know how tall she should be, her hair colour, anything. Why are you like this, author?
I find that describing more than one character in detail really kills the pacing of a scene - and even describing one character requires a moment of downtime in order to fit in. So for example, if I have three characters, I’ll describe one in detail and the other two in passing in the first scene, and then in later scenes I’ll find a slow moment to describe the other two.