Assuming you’ve put in adequate training, pacing is the most important consideration when it comes to racing well.
Sleep, your race nutrition, hydration, gear, etc. All are secondary to proper pacing.
Having perfect calorie intake during a marathon can not save you from running the first 10k too fast. But, pacing can salvage a marathon that you didn’t eat adequately during or before.
The final 10k of a marathon is full of people barely shuffling forward who “had a great first half”.
Below is my general pacing strategy that can work for just about every race distance!
The first third:
Run this fairly easy, it’s ok to let people pass you. Even during a race, what you feel to be easy will be faster than your general running pace.
The middle third:
Speed up a bit to a hard but controlled effort. You’ll likely repass a few people. Your pace may or may not increase.
The final third:
Best effort. You’ll pass people who took off at the beginning and have since expired. You may throw up. Your only salvation (and my race mantra) is that “the faster I run the sooner the pain will end.”