Change of life : what is the best fresh start ever ?

Hi guys, I’m about to quit my job (today is my last day at the office), to finish my degree in Computer Science. I’d like to take that opportunity to make a fresh start in my GTD system, my working habits, and my life in general. Here’s my question : what is the single new habit you took that dramatically changed your way of doing things, in work and in life ? I’m not looking for a silver bullet here, just someting easy that gets me on the right track for that new route in life I’m taking. Thanks in advance,