Good mind sets to have:
“Don’t get hit” - Isai, SSBM. Kinda like what insanelee is saying, it’s basically not losing. The first step to losing is getting hit, so, don’t get hit.
“I dunno, I just play” - DieSuperFly, SSBM. It’s as simple as that, just play. You know what to do when the situation arrises so just do it, thinking about this being a tournament match or thinking ANYTHING else besides playing your actual match will throw you off so much.
“Finally, I’m here!” - Me, SSBM. I took this mind set when I went to FC3. My friends and I drove 33 hours from Arizona to Indiana, when I arrived at the tournament, that’s all I was thinking. I was so happy to be out of the car and so excited to play the game I raped everyone, hard. You see, sometimes whatever game you play gets boring, or there are things that you hate about it, things like that can ruin your motivation. After 33 hours in a car I was just too excited to care about anything I didn’t like about the game and I just played. The tournament lasted 2 days but I was the talk of the tourney the rest of time simply from my beginning performance.