The Day Before a Tournament - What Should You Be Doing?

It's the day before a tournament. It's a nice enough day, you've gotten through your obligations-- be it school, work, a summer camp, or summer classes-- and now you can have time for Pokémon. What should you be doing? Is it worth restructuring your entire team in a moment of panic, in which you worry that your team can never be "good enough" for competitive? (The answer is no.) Well, I can't give a "master process" for what you should be doing, since every situation is different, but I can give a general process:

1) Breathe. It's just a tournament; it isn't the apocalypse. Whether you're participating in the early-season Friendlies or getting ready to go to a national championship, just remember: if you lose, it isn't the end of the world. You can't win every match you participate in, because you and your opponent are both human beings; I'm not just talking about tournaments (because sometimes you'll get very lucky and end up winning a lot of your matches), I'm talking about anything competitive that uses matches.
2) Realize that losing is just as beneficial as winning. If you lose, it might be because of type match-ups, tactics, specific Pokémon, Pokémon eugenics, luck, or most anything you can think of. Losing doesn't mean that you're "bad" with Pokémon. It doesn't necessarily mean that something is wrong with your team.
3) Psych yourself up! You can't go into a tournament with a bad attitude and expect to perform your best. Don't sulk and think, "I'm going to lose all of my games," because it can affect your performance. I'd also recommend against thinking that you're going to win all of your games, because you may just end up very disappointed. Be prepared to win, and be prepared to lose. That way, there are no surprises.
4) Perform a last check of your team. Is everyone in your Battle Box/party (depending on how you're participating in a tournament, it varies), and in the order that you want them in? Are held items correct, and beneficial for the Pokémon? Are moves organized how you want them to be organized? Make absolutely sure that your team is how you want it to be.

This may happen on the day of, or the day before (#6 is usually the day the tourney starts):

5) Lock in your party/Battle Box. For online tournaments, this involves registering your Battle Box, which makes it so that your team cannot be changed. For offline tournaments, you might want to go get an organizer/ref to check your Battle Box or party (which usually just involves showing them your team; you don't need to give them your system, you just need to show them what you've got so that they know that you aren't doing anything illegal.
6) Be assigned and find your first opponent, and have fun! Sportspersonship is key, because whether you win or lose, the purpose is to have fun; not to do well. Doing well is a rare treat, but it's your choice as to whether you have fun or not. You can lose a battle and still have fun!