It looks like you're trying to avoid the 'subject in the centre' syndrome...which is good. But simply putting the subject off-centre like this...isn't always the best solution. You really need to consider the rest of the scene and decide if it helps the image or not...and also decide how much of the 'background' you want to include or not include.
In this shot, I do like the contrast between the out of focus background and the image in the mirror...but I have to ask whether or not including all that background is helping. I don't think it is. I think you could get the same effect by only including a little bit of background around the mirror...and by doing that, you can practically 'fill the frame' with the mirror...which is to say that you're filling the subject with the interesting parts, rather than filling it full of background. It doesn't have to be cropped in and centred...you can still use an off-centre composition.