Berserker sued up what I was going to say, just thought I should add on to what's already been said. Don't let the other player's reputations get to you; in Smash, anything can and will happen out there, especially when everyone leasts expects it. Just stay calm and play your best. Don't be afraid to reach out to others, it's also a way to improve and meet other members of the community.
As for gameplay, make sure you know your range, know when to use an art and take advantage of it, and also remember your visions. A well-timed vision can get you out of almost anything. Match-up wise, watch-out for those floaty characters (Kirby, Jigglypuff, King Dedede, ect..); these guys can drive you nuts as they'll try to recover in a place where it's risky for Shulk to edge-guard outside of Jump. (Usually around the bottom of the stage, but sometimes, they like to air-dodge their way towards the edge, so you might want to watch-out for that)
I think you know the rest for the tournament tomorrow (Rest-up, you don't want to be functioning at drowsyness), but we can also try to give you some more pointers if you'd like.
You got this man. Go out there and show them the power of the Monado!