I find that not letting wins and loses get to you is one of the most important things you have to accomplish. Not letting the loses get to you is obvious, but the wins can get you too! I think having a plan to each matchups and being able to modify it to match the map you are playing is the trick.
After a couple of loses it is easy to get angry and then you start gambling. I.e. you’ll not play safe enough hoping to get ahead by cutting corners or you’ll over defend all set on not getting wiped out early. Either will cause you more loses.
Winning a lot builds confidence and suddenly you are not playing against an opponent, but just by yourself. And something this opponent does may be totally unexpected and even if you did see it coming, you did nothing to handle it since you were mentally in a whole other game.
The important thing is to treat each game as a new game. Being alert and aware of the signs you see from your opponent as well as sticking to your plan.