Set a realistic goal based on your current fitness level and chalk out the training plan working backwards.
Follow The Principles of Training like, Overload, Progression & Variability, Specificity, Recovery & Restoration & Periodization etc.
Train first for distance, only later for speed.
Alternate Hard & Easy Training.
Train frequently all year round.
Include at least One Speed Workout, One HIIT, One Tempo / Uphill / Fartlek Workout and One Long Run a week.
Include Running Specific Drills & Plyometrics in your Warm ups to improve strength & speed.
For Beginner runners just looking to finish, the amount of time spent running is the most important factor in training. So one should train accordingly.
For the Advanced runners, the physiological demands of the HM mimic that of the 10 K distance. From an energy system stand point, the 10 K is about 95% Aerobic & 5% Anaerobic. While the HM is 98% Aerobic & 2% Anaerobic. This means runners training to run faster & improve their times must include lots of Aerobic threshold & HM paced runs in their schedule.
Start your Race specific training Six weeks out from your Goal Race after a solid base building period, because after Four to Six weeks your form gradually reduces. Peaking at the right time is very important for improving your performance.