Check the bike over while the shops are still open
Have breakfast at least 2 hrs before the start
Wear enough, bur use things like gillets that you can take of if it warms up
Take enough drink (whatever your preference of sports drink is)
Take a few energy bars/jelly babies etc
Don't try to hang onto groups that put you under stress early on
Try to find a group that's just right for you
Chunk up the ride into sections and focus on just completing each section
HAVE FUN