Last season was the first time since season 5 i fully started and played every game. The first game i was a nervous wreck and did terrible, my hands were actually shaking in pregame. I went back and rewatched my demo and literally picked apart everything i know i did wrong. I felt a lot better realizing i made stupid mistakes and pinpointing them so they didn't happen again. 2nd match, still nervous, but i had a game plan and did much better. Like anything, it's more mental than you think. Few people can just go into something balls out and do good (and we're not just talking about video games).
Biggest thing to remember - everyone has played bad at some point or another. It happens to everyone - it's inevitable. It's all about what you do to improve that will make you successful or not.