Mine is simply this:
In order of increasing from least to most importance in your training (running, cycling, swimming, etc):
1. Quantity - how much you're doing
2. Quality - how you're doing the quantity
3. Intensity - how fast you're doing the quality
4. Recovery - most important - if you're not recovering you will stay in a kind of adaptation failure state constantly and the first three won't do for you what they're supposed to do. This is sort of built into the quantity, the quality, and the intensity. Recovery involves learning what to do in the hour following a hard workout, race, long run, etc. It involves understanding things like icing sore areas, using compression gear, physical therapy based stuff to keep the body recovering. It also involves learning to eat for repair, not just fuel, and also how important 8-10hours of unbroken sleep a day is.
I lived by those principles and also the following three rules, using them the few times I coached (mainly high school, one year of volunteer college coaching for a small D2, now a D3, school). All the athletes I helped progressed and remained less injured/fatigued.
1 in 10: during base work take one complete day off every ten days (from running, can still x-train)
1 in 7: during peak workout/racing part of season, take one complete day of every 7 days (from running, can still x-train on that day)
1 in 3: no more than one out of every three workouts shall be 'hard' - this includes long runs because a long run is more time biomechanically stress loading the body (more steps)
These 'rules' were to get runners to recognize that it is in recovery the body adapts - and that often increasing too fast or not taking days off leads to repetitive stress based injuries, the most common among endurance athletes - body just needs a break from time to time and will thank you later. I think that a lot of high school and college runners 'race' poorly even though their training shows they should be racing faster...because they aren't recovering properly...just my 'bro' two cents.