Preface: I have partial face-blindness (how does it work? There's a explanation in this Q&A!), which means that even though I strive to make each character distinct and different from the others, I sometimes am unable to because my dumb brain trips me up. It's not same-face syndrome so much as it is my brain getting stuck on a particular way to draw a thing, and unconsciously replicating it (like, only drawing people gritting their teeth for 3 chapters straight >.<).
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I try to draw a wide range of characters on the pretty-plain-ugly scale! I like to vary it as much as I am able, because it's more fun to me that way. Drawing pretty people is a lot of fun - but so is drawing ugly people, and plain people! I like drawing people who are a mix of these things - people who have very pretty hair, but quite plain faces, or very pretty faces but they've not bothered to shave this morning so it's covered in stubble, etc., etc. Also, my metric for what is "pretty" might be different than that of other people.
I try to suit the physical looks to the personality, and I like to contrast two different physical types with each other - i.e: designing in pairs. Or trios. Let's use visual examples!
These three dorks are in my comic, and mostly appear in scenes together - either as a complete trio, or in some constellation of duo. From the top, they are Kazue, Chouko and Dateh. They're all wearing similar colours (because it's kind of a uniform, with personal tweaks), but they're all distinctly different, physically. Kazue is tiny, all slim and narrow and fairly straight lines, with a slightly elongated triangle shape to her face; she's also very flatchested and narrow across the hips. Chouko is a head taller than she is, with longer hair, a more heart-shaped face, and a more hourglass-shaped figure - broader in the hips and shoulders than Kazue - and her nose is broader and so is her mouth, and she's got more obviously visible eyelashes. Dateh is taller than both of them, and made of heavy, softer shapes, with a very square face and heavier features.
They all contrast with each other in some way - in height, in face-shape, in general body type, etc., etc. - and it lets me draw them all without ever getting bored at repetition.
(also I think they're all pretty cute but I am biased because I'm their mom)
Anyway, variety is the spice of life and also more fun to draw.