Someone wrote to me and said he'd read somewhere that you should move the mirror to the right, not the left, and asked me what is really the best. Here is my answer:
The best direction to go in is what is best for you. Apparently everyone has their own "timeline" arranged in a particular way. Often the past is to their right and the future is to their left. For some, the past is behind them and the future is in front of them.
Ideally, you would do the mirror exercise in a way that matches the natural way your timeline is arranged.
Here's how to know: Close your eyes and imagine a future event. Picture something you think is going to happen. Where is it? If you had to say where that image appears to you, where would you say it is?
Now close your eyes and remember something that happened to you. Where does that image seem to appear?
Go back and forth like this a few times, and you should have a pretty good idea that for you, the future is in a particular place (in front of you, to your right or left, etc.), and the past is in a different position in your mind.
Now you can do the mirror exercise in a way that matches your own internal organization.