Know what's coming before you sit down.
Every campaign player is handed a random pregenerated character at the table — level 3 when you sit down, level 6 by the end of the campaign.
You won't know who you're playing until the con, so the best prep is breadth: get a feel for how the classes play rather than mastering one build.
All tables run the 2024 Player's Handbook (the revised fifth edition). If you learned on 2014 rules you'll be fine — the changes worth knowing: weapon masteries, reworked species and backgrounds, and updated spells. The 2024 Basic Rules are free to read on D&D Beyond.
Nothing required — dice, sheets, and pencils are provided at every table. Your favorite dice are welcome.