Reflection is an important part of any journey. It is the careful consideration of your journey, your goals and yourself. If you try to attempt self-improvement without reflection, I don't think you're going to get very far at all. Or at the very most, your results will be a little skewed
How you choose to do your reflection is up to you, but daily seems to be the most recommended frequency. I'm not good at reflecting daily, but every time I deem that it's time to make another change to the way I live my life I take a moment to consider my decision and the possibilities. I reflect after a bad day - trying to examine ways I could have affected the outcome of the day for the better. I take the time to reflect upon my beliefs - especially when I find them being questioned.
A little reflection can go a long way. It's good for the mind and the soul. Looking back and looking forward - the self improvement version of looking both ways before you cross the street.