Ideally, I'd like to team up with somebody who actually seriously would like to improve his/her English (maybe studying for exams or something), because I'd like to work on my Chinese at a pretty intense pace, too. So, think more "a language lesson exchange" rather than "a casual chat about your hobbies etc". For what it's worth, I got the English teaching certificate too. I don't work here as a teacher though.
I live in Shuangjing and I work pretty long hours, so it'd be best if you lived in this part of Beijing too, because I'd like to meet up on weekday evenings..
Just send me a message if you think this would work for you...