There is no right way or wrong way to approach the subject.
So far all of the advice is good. It is how you feel comfortable in approaching the subject.
Even if you suggest a bit of light bondage or spanking and see how she reacts to that.

You relationship is relatively new and just starting out. If you really want to pursue your submissive side then it is best to communicate your feelings with her, and get it out instead of continually waiting. It becomes harder to do the longer you wait.
Don't wait for the right moment or the right time. It doesn't really happen that way.