Hmmm, i've looked in a mirror before, but it wasn't lucid...it was a very vivid dream though...not to frighten you, but i didn't see myself, i saw someone else in the dream.
In interpreting it, the person i saw in the mirror that wasn't myself, i took that to be some aspect of my character that i needed to pay more attention to.
Don't be scared of what you might see, just go with it, and see how it makes you feel. You can learn something.
Also, being as it's a lucid dream, if you don't like what you see, you can change it.
In my case, not being lucid, i was forced to 'confront' an aspect of myself...
Hope this helps!
By the way, welcome to the board, feel free to Pm me or any other dreamguide (the ones in green) if you have any more questions!!