0. See if you can Preregister
So important, it's number zero on my list! Not every store will be taking preregistrations for the Prerelease, but if they are it's always a good idea to sign up ahead of time and save your spot. This ensures you don't miss out in case it fills up before you arrive the morning of the event!
1. Have Fun
Prerelease events are meant to be two important things to players. Firstly, they're meant to be the very first opportunity for players to play with Magic's newest cards. Secondly they're meant to be fun and relaxed events!
2. Be Helpful
Normally during a tournament helping other players build their deck is forbidden, but during Prereleases because of the new cards and mechanics, rather than forbid it - we encourage players to help each other during deck building. Maybe your friend sees a card combo you missed, or maybe you're not sure what your twenty-third card should be.
3. Change your deck
Throughout a normal tournament, your deck should remain the same, including de-sideboarding between rounds. But at a Prerelease decks are much more amorphous, you might add a card after a game and discover it's way better than you realized. Well, during the Prerelease you can keep it in! Or maybe after the first or second round you decide to change your deck up, maybe you see a friend playing Blue and you recognize a few cards you're not playing - you can completely change your deck between rounds!
To those of you heading to a Prerelease this weekend, have fun! I hope you open lots of awesome and fun cards!