Evaluating your work

I was sitting eating lunch flicking through some photos I'd taken and was wondering how I evaluate my own work.  How do I judge whether something is good or not.  Is it that it matches some compositional rules?  That friends or family like it?  That it's similar in style or tone to photographers I admire?

I'd hope that as I take more photos that i'd continue to improve.  Does that mean that photos I think are good today, I may dislike in the future?

How do you test your photos?