I get rid of tourney nerves by telling myself I suck and that I WILL lose the next match, this may sound silly but it got me second at a major :P
The idea is that if you are hard on yourself like that, the second you win your first match all of your nerves disappear, I can't say why that is but this has been the case for me, and the only time my nerves came back was when I had to fight HeartNana in finals due to him kinda being like a hero figure for me early on, I couldn't even do the standard Noel BnB off of drive it was so bad :|