Have a training plan
Even a free one-size-fits-all training plan that you can download is good (find sample plans at we-run.co.uk). They help you build up your distance safely, and remind you to plan in enough rest and recovery days.
Don’t go too fast on your longer training runs
These practice runs are about building endurance, not speed. Aim for a gentle pace where you can hold a conversation. If you struggle, you will get demotivated. Use your shorter runs for speed training. Most people do three training runs a week.
Do regular injury-proofing exercises
Squats, lunges, planks and bridge strengthen legs and core. Do 5 to 10 minutes a day, or half an hour a few times a week.
Don’t explode out of the starting gate
As the race day approaches, remember that you will be full of adrenaline, so it will be tempting to go off too fast. You will pay for it later as your energy levels flag. Studies show that it is best to run the first half more slowly than the second.