For a short distance like 5K the key factor is quality not quantity. Decide what your desired time is then use a pace calculator to work out your target split times. A good approach for a 5K, in terms of preparation training, would be 3 sessions a week which include a slow day (6 min/k), a interval day (mix of slow and fast 2 min runs, keep the fast and slow times the same if possible, naturally the distance covered will differ) and a target pace day (example, 5 min/k).This schedule can repeat for any number of weeks until the target time is reached. Varying your course is also very important so that you have a good balance of hills and flat, remember the race route will change every event so training on a flat route and racing in the mountains is going to be very difficult.