The single most useful piece of advice I received recently is this: START BEFORE YOU'RE READY. Genius! Not exactly a new concept but that's not the point.
Consciously or not, we all use this excuse all too frequently: I am not ready (to quit the job, to start exercising, to get married, to have children, to start a business, to take the leap of faith...).
I know I do: it took me 18 months to leave my last job which I loved, but which was not good for me. Then I finally did it (more or less jumped with my eyes closed) and haven't looked back.
Not ready means: playing a waiting game, procrastinating, wasting time, being 'stuck in the mediocrity of the masses' (oops!)... start before you're ready is the answer because 'ready' might never come otherwise.
I started implementing this advice over the last week or so, and something pretty amazing started happening. Suddenly, I became ready!! Because I put myself in situations where I had no other choice but to GET READY!
Give it a go, I cannot recommend it enough :)