Here are my Sutras (rules/best practices) for long distance running.

(Disclaimer: I am not an expert. This is what I have learnt from reading, trying to practice and found it useful. Your thoughts are welcome!)

1) Focus on Breath: While running, keep focus on your breath. Ask yourself: can I keep this pace of breath for next 10, 20 40 km?

2) How to Breath!: Breath into your stomach/abdomen.
Preferrably breath in through nose for 3 steps. Breathing in through nose heats the air to a suitable temparature for your lungs.
Breath out from nose+mouth for 2 steps, to empty all air from your lungs.
Refer this page for more details on 3:2 breathing technique: marathon breathing technique.
(Suggestion: Try Yoga/Pranayama to improve breathing: KapaalaBhaati and Agni saara Kriya)

3) Foot work: Each step should land on the ball of your foot (just behind the toes) and not on the heels.
(Suggestion: I try to practice POSE method. See Here and Here.)

4) Pace: Research says the best runners have a pace of around 180 steps per minute at the peak performance in long distance running. According to POSE running technique, keep the stride small, so that your knees do not need to take more pressure and vary the pace depending on the speed you can keep up with. Refer: http://posetech.com

5) Days before the race: Start stocking yourself with more corbohydrates much before the race day. (Suggestion: Rice Items, Pasta, Banana Milkshake etc.)

6) Race Day:
Before the Race: Just jog for some time and streatch very slightly, if at all you want to stretch. Many sites say, stretching too much before the race makes your muscle loose and which might cause injury.

During the race Continue to drink water/sports drinks frequently. Don't over drink water, but just sufficient so that you don't feel thirsty. No harm is eating oranges and banana during the race.

After the race: Do some streatching after the run, which reduces buildup of pain.Typical exerciese:
- Forward and back bends, see Padangusthasana and Prasarita Padottanasana
- Side stretch, See Virabhadrasana I, Virabhadrasana II, Virabhadrasana III
- Trikonasana
- Eka Paada Raja Kapotasana (One leg King Piegon Pose)

7) After the race: Continue to drink water/sports drink, eat banana (provides carbohydrates and importantly salts which avoid muscle cramps). Eat food rich in carbohydrates and protein, within 20 minutes of the race so that you don't feel too much tired after wards. Rice-Dhal items, Idly etc are good.

8) Marathon is a race against yourself. Don't compare with others.
Do your best. Do it smiling!

9) Last, but not the least: Avoid Injuries. Knees, ankel and back are the ones which you should observe. Muscle pain and fatigue are common. But listen to your body. If you feel you are hurting yourself, slow down and observe. If you are still hurting, keep your ego aside and discontinue the run!

Your comments and feedbacks are welcome!