If you want to run a faster 5k I suggest doing this on a weekly basis.
Day 1- 35-45 minutes at what YOU consider a strong but manageable pace-
2-repeat 800s OR miles OR any kind of interval/speed work
3-40-55 minutes at a good pace
4-35-45
5-speed work
6-long run
7-rest
This is a good balance of speed and mileage for a 5k, and it gets maintains its difficulty because its based in time run not mileage. Look up speed workouts, there are a ton.