Melee, PM, or Smash 4?
At the tournament, be sure to ask questions. Not just to the Tournament Organizer, but to everyone who plays. Asking questions and becoming friends with people will help you. Try to get many friendly games in. Practicing will always help. This also helps you find friends. Getting friends there means more friendlies. More friendlies = more practice. If you lose, ask how you can improve. Hand shake or fist bump, or whatever it is at the beginning and after a set. Say something nice before playing like "Good Luck" or "Lets have fun" also say good games after a set. Also, it is good to talk to the top players there. If you can get them to talk to you, you can get friendlies with them, and may become friends with them. And, if you play against them and lose, be sure to ask how you can improve later. Don't be afraid to ask to join something. I saw 2 people doing friendlies and I wanted to play as well, but got too scared. The next time, I asked if we could rotate and they welcomed me as much as my Mexican relatives would have. Also bring water. Matches will get intense and you will need something to drink.
That is all I can think of for right now.