Two things. Just because your character is self-centered, doesn't mean she can't take notice of what other characters are doing. Just have her mention things in passing, and/or belittle the actions of others. Let the actions of other characters speak for themselves.
The other thing is that I think that it is admirable to write a story where you hamper your strengths. I used to play chess with my grandma's husband whenever I would go over there, and he always beat me. But one thing that he did to really help me was point out a very interesting detail. He told me that I overused my knights, and that it ended up being a major weakness for me. So, for a while, he would make me play without my knights. I found that it made me a much better chess player because I used all the pieces in my strategy instead of just one. Having read one of your stories, I would say that you are very good at characterization. But writing a story where characterization is toned down a bit should help you develop your other writing skills and styles, and make you a much better writer.