In my writing I've come to realize I use the letter J to start names ALOT. Jared, Jin, and Jonas are just to name a few. Upon realizing this I tried to avoid J names to break the habit and promptly switched to names ending with adon. It took me a bit to realize that one too. Perhaps it's just a comfortable rut I got stuck into but it is very difficult to break. My newest characters have names randomly chosen. (I ask my husband for a letter or series of such and then play with it until I like one.) It's quite amusing.
Are there any ruts you get stuck in?