How can i excell in my cricket? I am an eighth grader who dreams of playing in his country.?

We're having team tryouts this wednesday, most of my friends are favorites for selections but i am a shoe in. I starting playing last year and you wouldn't believe how pathetic i was, a lot of improvement has taken place but not enough to get me in the team. I can play well at times, i can also play steadily and take singles, but some times i am a horrific failure, i have a nerves problem. Can you give me some tips to help, i'll be really grateful.