Racing speed develops in many ways: through long runs, threshold runs, weight work, speedwork and slow, easy runs. All of these are ingredients of a sensible training program.
Here are some pacing guidelines for various types of training runs:
- During long runs, stay somewhere between 1:35 and 1:45 per mile slower than your current 5K race pace.
- For threshold runs, try to run 20 to 40 seconds per mile slower than your 5K pace.
- When doing speedwork, try to run 800s at 5K pace, and 400s and shorter distances as much as 10 seconds per mile faster than 5K pace.
- On easy/recovery days, run at least two minutes per mile slower than your 5K race pace. Your legs will thank you.
Day-to-day runs do not need to be done at a given pace to improve racing speed. The most important rule is to pay close attention to how your body and legs feel. When you're tired, ease back even more than usual on your easy/recovery runs.
Whether or not you reach your goal times depends on talent and luck to a degree, but smart training will take you much farther than bashing your body day after day. Good luck.