Same face syndrome drives me batty @u@ Unless your characters are all siblings or something, put more variance into the faces! The whole face, not just "These two characters have different eye shapes".
On the same topic of faces, it irks me when character emotions are essentially iconic "^ _ ^" "O _ O" "> _ >". Expressions shouldn't look like they're projected onto a flat face-sceen. There's muscles and fat and stuff, which move and pinch and stretch with expressions. I like when artists aren't afraid to make their character pull a silly or extreme facial expression, even if it means they won't look beautiful and perfect.
Also ditto western artists making right-to-left comics. To me, it says the artists is copying the surface look of manga without understanding the function, thus making it less accessible to their reader. And if an artist just does it to mimic the manga look, chances are they're copying a lot of other surface-level stuff (like the odd translations). If a design decision unintentionally throws your readers off, even for a moment, you're better off avoiding it.