A bit of a personal one from the 2 of us here. The Half Marathon was the first long-distance race either of us attempted. Coming out of school as pretty accomplished track athletes, I guess we naively believed that qualified us to comfortably run the 21.1km. Safe to say, neither of us trained properly and it was although we both came home with finishers medals, it was not pretty and we couldn't walk for a week.
The lesson here is a simple one. Find a good training plan and stick to it. Everything matters here. Getting in those long runs are key to prepare for the rigours of going the distance, and the speed/tempo sessions will build up your cardio-vascular endurance. Put all these pieces together and you'll have no problems finishing, and finishing comfortably.
Ready to get started on your journey?