Make sure you know exactly where it is arrive early and travel in a suit. Find the dressing room early. If it is a finals day where there are several games taking place you don't really need to get in touch with your assistants but if it is one off game I would give them a quick call or text just to say hello. When your NARs arrive choose a senior assistant to do all subs etc and controlling the benches. You will tell who you want as your senior. Briefing just be clear, you have 2 refs so they will know what is expected of them. A lot of the breifing will come from the chatting before the game, good NARs will ask about specifics ie bookings penaltys and how you want to deal with those. Do your pitch inspection as a team, you do the balls let your Ars do the nets and let them do the equipment check.
Make sure you introduce yourself and your team to both sets of coaches before the game.
The game is their Champions league final. Do not be afraid to use your whistle, and if needed use your cards do not think I can't use my cards because it is a final. ( i gave out 5 in a final last week at U14s)
As your a level 8 I am guessing this is a youth final. If I am wrong ignore this, but the parents will be loud, every decision you give will be wrong.
Do what you have been doing all season and you will be fine. Use your NARs for advice if you feel you need to, it is not a weakness but shows good game management and enjoy it. You have been chosen because the "suits" think you are good enough for this game and you are.
Confidence good strong signals and talk to the players and you will be fine.
Lets us know how you get on.
Any specific questions just ask and there will always be some one here to answer.
Good Luck, I have probably missed out loads of things but the rest of the guys will make up for my omisions.