I've shared this story on SALT a few times at this point, but I still chalk it up as one of my biggest financial successes.
A few months after starting work here (and really started reading about my loans), I decided to triple the amount I paid on them each month. I could afford to do so, but I simply hadn't to that point because I didn't understand the power of cutting down on accruing interest. As a result of this decision, I shaved a few years and more than $1,000 off my balance.
Also, I got to see this a lot sooner, too, which was definitely worth it!