Oh man. I feel pretty confident about my faces most of the time, but I deeeefinitely feel similarly to @sophiekaldinski -- I have almost a "default" body type that I'll tend towards if I'm not actively striving to do something different (though I'm the opposite in that a lot of my boys tend to be scrawny, haha!)
I have only in the past couple of years really started to branch out in terms of taking an effort to NOT MAKE EVERYONE WHITE, and man, that has helped a lot -- there's so many more design options when I started asking "well, could this character be a different race/ethnicity?" that I can't believe I've been ignoring all this time. xD
An exercise that actually helped me out a bunch was this "character variety" meme I found once on Deviantart -- I just crammed all my characters in there instead of comparing two specific ones, and it helped me get a good idea of which characters didn't really have a distinct look or feel. I'd definitely recommend it if you're looking to explore that sort of thing!
My favourite dumb detail that nobody thinks about is actually ......teeth? An underbite or overbite changes the whole shape of a character's face, and weirdly implies a lot about their personality for such a tiny change. I love seeing imperfect teeth or an imperfect bite in other characters. IT'S A TINY DETAIL and not as big a deal as like....silhouette and body type, but it's my favourite tiny detail. :>