Focus on having fun. Fun. KEEP FUN IN MIND all day!!!
Time goes faster and the ride is more fun with the distraction of riding with friends.
Don’t think about the whole thing, just what you need to do to get to your next 10 miles, for instance. When you have ~30 miles left, you know you can do that since you’ve ridden 30 mile group rides no problem in the past!
Take a bite of food or drink water every 15 minutes. Set an alarm on your GPS computer to call your attention to this. Make sure you have both carbs and plenty of electrolytes going into your body. Think 60-90 grams of carbs per hour and 1 bottle of water per hour depending on the temp of the day.
If you get chafed anywhere on your shorter rides, it’ll be especially bad on a long ride.
Get out of the saddle on climbs sometimes, shift position with your hands on the handlebars, look all around.
Try to keep your exertion in the realm of heart rate not too high such that you can carry on a conversation. If you can talk, your heart is not beating too much. Stay in this range all day!
Lingering and eating too much at once can make it painful when it’s time to resume riding. This is an opportunity to stretch too and move around. Don’t sit down.
Pushing high (harder) gears will wear out your muscles faster than spinning lower (easier) gears. You can eat and fuel for endurance, but once your muscles are tired, it’s hard to keep moving.
Carb loading is not what it sounds like, don’t do it. You’re better off eating salad and a balanced, wholesome dinner than a huge bowl of pasta since you’ll sleep better after the wholesome meal.
Do NOT start hungry. Minimize heavy proteins like meat. Carbs such as oatmeal and fruits are good. But don’t eat a breakfast your body isn’t used to, either.
Today isn’t the day to experiment with new saddles, new bike position, new clothes, new nutrition, new anything.
Even the most obvious things you need to bring with you, things you need to do, and what you should load in your pockets and saddle bag are EASILY forgotten on the big day. Make a checklist to allow your brain to focus on fun and not worry/waste energy having to think.
HAVE FUN!!!
The overarching principle is: have fun! If you’ll have more fun by breaking one of these rules, then break the rule.