I'd like to add one insight to the immense amount of information out there about SMART goal-setting and the like. Make the goal squirmy.
A squirmy goal is exactly what it sounds like: it's a goal that makes you squirm in your seat. It's the kind of goal that makes you groan because it has that perfect blend of just-beyond-your-comfort-zone but achievable if you really go for it.
In grad school, my program director was a master of making me squirm. He would paint these big, bombastic visions of high mountain-top places we could summit in our careers if we really wanted to. His inspirational speeches were meant to expand our vision of what was possible for our lives, but in the process filled me with so much tension. It made me pretty sore at the time, but I've come to realize how powerful those visions are for creating reality.
Over-sized goals don't make you squirm, because you don't know enough about them to freak out. The challenge is to honestly assess reality and commit to journeys just outside the edge of your competency. Challenges that make you mumble "here we go again."