Take a look at some of your old SUs. Is there any recurring or overlapping traits that are prevalent in your characters? It could be a name you constantly use, or a certain consistent appearance they have, or a certain personality type? Perhaps something a bit more subtle?
I always find that most of my characters have bits and pieces of myself in it, the ones who I see as being stronger character based are the ones that have more of me in them. Aside from this, I went through phases, first was the Japanese phase where practically all my characters were Japanese, then there was the Russian phase, now, I think I'm onto the British phase, although Atlantis Arising has a multi-cultural line up of side characters. I use to make some pretty dark characters as well, but I never really quite got a hold on the whole "psychopathic" character, I try every once and a while, but often these characters are quite flawed when I RP them.
Also noted that most of my characters are never really "short" in height, and are mostly average to muscular build. Also, many seem to have some sort of eye disorder, colour blind, Heterochromia, glasses, etc.
How do you generally create your characters? Do you enjoy making multiple characters, a new one for each roleplay? Or do you stick with one character throughout?
I use to use practically the same character for almost every roleplay I was in, but now I like to create new characters for each new roleplay I enter, roleplaying as something different each time. I also find it helps to expand my character base, giving me a wider diversity of characters rather than sticking to one niche.