"If you want to do something you'll find a way, if you don't you'll find an excuse."
I love motivational aphorisms, and this is my absolute favorite. So much so that it's on my laptop's screen saver.
It really speaks to me because, for me at least, it cuts both ways. It's 100% true for me, in that it reflects both the best and the worst of my character.
Since that quote says it all, I'm not going to belabour the obvious here. I'll just say that central to making big positive changes in your life is to figure out exactly what you really want. Not what you kind-of want in a vague, half-assed way, nor what it's hip or fashionable to want. No, find out what you really want, and once you know that you'll do the things to need to do to get it.