How to Keep Your Cool (Riot Advice Please!)

I Know there have been discussions like this in the past but nothing recent. In the end, where the answers most likely don't differ from the past i would like some constructive criticism if you like to. Look up my games and see. Anyway my problem when you look at my stats and in games and such is I do great in normal's, with the occasional loss, but as SOON as i play ranked things go sour. I play like I'm new to the game and get nervous. How can i overcome this....my mind mentally fights me in this and always has. Thanks guys.