Finishing a race is decided by months of mileage. How to build distance, structure a week, set your pace, train eating and drinking, and race-day checks.
The most common cause of running injury is not intensity but a sudden jump in distance. Raise weekly total mileage only a little at a time, and drop it every third or fourth week for recovery. Enduring the training and recovering from it are different things, and mileage piled on too fast tends to return as an injury before the race.
Mixing runs with different jobs beats repeating the same distance at the same pace every day. Fill most of your mileage at a pace where you could hold a conversation, and keep fast work to once or twice a week. Running your long sessions in your race-day kit and shoes is good practice too.
The most common race mistake is going out too fast. Crowds and excitement pull you above your usual pace, and time gained early is lost several times over late. Set a target pace from what your training actually shows, and run the first few kilometres slower than that. A watch's pace readout can swing wildly between buildings or in tunnels, so adjust using split times together with how you feel.
Long distances require fluid and carbohydrate along the way. What works, and when, differs by person, so test it during long training runs. Anything eaten for the first time on race day risks an unhappy stomach. The same goes for shoes and clothing: new gear on the day invites blisters. For a race on a hot day you also lose a lot of salt through sweat, so test salty fuel during long training runs as well.
Reducing mileage in the final weeks to shed accumulated fatigue is standard. Nerves push you to run more, but extra training at this point adds no fitness and only leaves you tired. Sleep well, and keep the day before to a light loosening run at most.
For a first race, the most important thing is not to be greedy about distance. Even for people who already run regularly, a few weeks to two or three months is typical for 5 km and 10 km, longer for a half marathon and several months for a full marathon. If your running history is short, start with a 5 km or 10 km race to experience race-day atmosphere and pacing before moving up.
Race-day mistakes usually come not from lack of preparation but from doing something different from normal. Eat the breakfast you usually have before long runs a few hours before the start, and do not take unfamiliar fuel handed out on the course. Toilet queues are long, so arrive early, and on a chilly morning wear a throwaway layer until just before the start. Drink a little at each aid station, but there is no need to force down large amounts when you are not thirsty. If something feels wrong, put your body before your time and do not hesitate to ask the medical staff along the course for help.
Right after finishing, walk slowly to cool down rather than stopping and sitting at once, and eat something with carbohydrates and protein along with water. After a full marathon, muscles and tendons need time to repair, so walk lightly or rest for about a week, then bring your distance back gradually over the following weeks. Jumping straight into training for the next race on a post-race high is a shortcut to injury. Long-distance running puts heavy demands on the heart, so if you have cardiovascular disease or a family history of it, talk to a medical professional before training. Stop immediately if you feel chest pain or severe dizziness in training or racing.