Forget positive thinking ... forget thinking all together. Forget how you feel too. To be honest, they aren't essential to playing your best. In fact, they get in the way more than anything.
I know this is radical. It goes against almost everything you've heard, read and maybe even experienced. I mean, who hasn't played their best when they are focused and confident? But who is focused and confident all the time? No one. What do you do when your doubt, worry, and are scared, nervous, or angry? You do the right thing anyway.
The fact is what you DO on the field matters more than anything. You can win when you feel lousy. You can run fast when you feel tired. You can focus on the ball when you feel pressure.
Yes it is hard. Very hard. Doing when you don't want to or feel like it is what makes you mentally tough. Giving in to your thoughts and feelings is your weakness.
Get out of your mind - and concentrate on what you choose TO DO.
Here are some videoes that will help:
Do what you believe in
Live in the moment & give up control
Worry is good for you!
Power of convictions