When I had the time, I used to play each new game I got to death, mastering them and searching every inch for secrets or exploits. All the more so with games I loved. That's how I figured out ways to skip most of Dragon's Curse and Shapeshifter.
I got finishing the original Zelda down to around twenty minutes. Would get to the end of FFIII SNES in a day and a half, did timed runs of Phantasy Star and also maxed out the characters in most RPGs when it wasn't necessary. I submitted a winning high score to EGM for Bloody Wolf, but they never published it.
In grade six, every day day after school I hiked down to Zellers and played through Black Tiger on a single quarter. I took the long way through each stage, racking up all the points I could. Once I got to the final check point without dying, I'd walk around killing enemies until the timer ran out. On my last life, once the time was almost out, I'd finish the game and enter the hi score.