The real question, is shooting the mirror for what purpose. Usually a mirror is supposed to reflect "something". The question here is what do you want the mirror to reflect. If this is a product shot of a mirror, then it still needs to reflect something. Is there a model involved? If you choose to have her appear in the mirror, then you only need deal with what shows behind her.
I often shoot mirrors, and I just work around with the tilt of the mirror till in reflects something neutral and then I move a model into that scene. Otherwise, I cover the mirror surface with white paper, and then later on, put into the white area of the mirror what ever I want.
Here is an example using the white paper while the model was holding a mirror and then I put the model holding the mirror into the mirror and so forth.
Here is an example where I just provided a neutral background for the mirror. Since it contains a nude model, here's a link:
http://www.glamour1.com/photoplog/index.php?n=346
Cheers,
rfs