1.
Read the rules and understand what you need to do
2.
Read the long-distance riding tips
3. Checklists really help. Equipment checklist. Maintenance checklist. Gas station/DBR check checklist.
4. Take a test trip, mileage doesn't really matter, but treat it like a ride in terms of documentation.
5. Planning your route really helps.
6. Know the range of your bike and plan your gas stops around it. Way less stress than looking for gas stations while running on fumes. Have a buffer in case you run into headwinds, etc., that reduce your range. Don't be afraid to take extra gas stops if needed.
7. Know your limitations and know what parts of your body start to ache. Butt hurts after awhile? Get a buttpad. Back hurts after awhile? Consider a back brace. Legs cramping? Highway pegs, having a bike you can stand up on, and/or being able to move around on the bike (sitting on the pillion, etc.) helps.
8. Design a figure-8 ride for your first ride. Make a 500 mile loop back to your starting gas station and then evaluate yourself and the bike. Can you both continue? If so, do the second half of the figure-8.
9. There will be minor setbacks that occur during every ride. Cup holder randomly falling off while riding. Rain suddenly falling from a clear sky. >75% of the gas pumps you use don't have receipt paper.
In the end, it's totally worth it and you'll look back with fond memories. Good luck!