Always come prepared!! Although it may not seem like a big deal you'll never know what might be going on at your local venue or large scale tournament.
First is your attitude, understand that our community has a breadth of types of personality traits that meander about the venue. From the outwardly friendly newbie to the smelly frequenter who has the worst attitude you've ever encountered there are going to be a lot of people, just be kind to those you meet and understand that everyone is there for different reasons.
You'll want to always come prepared, bring a snack and lots of water (it'll help you focus a lot more than energy drinks or soda), and an extra controller in case yours breaks and the venue/friend cannot provide you with an extra.
Try to get friendlies in with whoever you can before the bracket starts and get a good grasp of the skill level of the players that are there, if it's something that might intimidate you it's just an option. Go into your matches knowing you're there to win, and don't let anything stop you!