1.) Always try to constantly put yourself in situations where you can feel that hardcore and intense pressure all the time, keep playing at tournaments, keep having people watch you play, etc.
2.) Always try to play with the situational pressure along with something on the line, it can be a money match, the tournament, or some sort of bet where you will face the outcome of losing something.
3.) Try to not always strive to ‘impress’ the crowd when you but yourself in these situations, just try to have fun, don’t put a big emphasis to win all the time. Sometimes, you can just try to fuck around a bit and don’t take it serious. Pick a character you don’t don’t normally play with or some shit, or just try to land a combo you’ve been working on, and if you lose, so what? Then after a while once you notice your nerves start to diminish, amp it up a bit.
4.) Like someone mentioned, keep your emotions at the door. Keep all your negative thoughts out of your head, and whenever they try to creep in, try your to replace that negative thought with something positive or neutral for you can concentrate. Always have thoughts of things you need to look out for when you play and anticipate various outcomes, options and choices your opponent can make for you can react accordingly.