A guide by Edi courtesy of Abge: https://tinyurl.com/TipsF2FDip
If you're successful, i.e., not eliminated, we're talking playing Diplomacy with out a break for a single second for 8:30am-3pm, 5:30pm-midnight. And then again 8:30am-3pm the next day. It's *extraordinarily* important to be well rested and well stocked up on snacks/water. And always plan to win, so no excuses.
80% of the people there have known each other and exclusively play F2F with their fellow hardcore F2F players for 10-30 years. That will be intimidating and annoying and that's OK.
Follow etiquette. Not that I don't expect you to, but just reinforcing it. Be quiet for board assignments, don't kibitz about other boards, don't be a dick, etc.
Practice writing orders. Not only the technical aspects (how do you show support move, support hold, hold, move; how do you designate coasts; how do you designate convoys; Bulgaria has SOUTH and EAST coasts, not SOUTH and NORTH coasts) but making sure they are legible both for your own sake and for the overall enjoyment and smoothness of the game for everyone involved.
Be aware of the scoring system. It will be Sum of Squares.
http://www.diplomaticcorps.org/Scoring/squares.html
TL;DR the more centers the better!; slightly better for you to be a 10 vs 3 and 3 and 3 than a 10 vs a 9.
Make friends! Have fun! (Give me Belgium)