What simply works?:
1. Easy miles. Lots of them. But EASY. Do as many as you can. If 60mpw is your max, that’s ok. 90-100 would be better. But EASY. You should feel you are reigning yourself in intentionally on these. If you’re not fresh and springy by the end, you did it wrong. If it negatively impacts your run the next day, you did it wrong. If you can’t do some snappy strides at the end, you did it wrong. If you’re tired for your workout days, you did it wrong.
Note: this exaggerates a bit as some days you will feel like dogshyt no matter what, but the point is huge and most people mess it up.
2. Consistency. Say you have 180 days until target race. It’s much more important to run 175 of those days than to overdo it and miss weeks with injury. If you feel a bad twinge, stop the workout. Walk home if needed.
When I was young, I would try to finish everything, and at the desired paces. Injuries galore. Remember: the goal is to run tomorrow.
3. Threshold. And lots of it. Huge bang for the buck. Hard enough to get huge aerobic benefits, easy enough to not destroy yourself. Do 25-30 minutes of work, divided up in different units to prevent boredom. 5x 5 minutes. 10x3 minutes. 20x90s. I advise measuring by time instead of distance so you focus on proper effort. Keep the rests 30 to 90s max.
4. Speed. Touch it at least weekly. 100s, 150s, 200s. Short hills.
5. Race pace. 600s and 1000s. You only need to do these the last 4-6 weeks before the goal race.
That’s it. Simple, but not easy.