- clean diet: you still need to get enough calories, but if you can minimize processed foods and junk food, it will go a long way
maximize sleep - unless you are a student or work from home, it is IMPOSSIBLE to sleep 40 hours a week. Going from 25 to low 30s hours of sleep a work week helped me a lot though, even with missing an occasional morning run
core - we haven't evolved to adapt to the sedentary lifestyle. Unless you lead wilderness hiking tours for your 40 hour a week job, your core is not strong enough from just running alone
none of these led to big benefits separately or in conjunction, just small, marked benefits of a few secs at 5/10 and half
I should include one more thing that seems obvious to me:
rest - running is your activity. Don't go do big hikes, ultimate, basketball, whatever. Just say no when people try to pressure you into doing this type of stuff. And don't replace runs with these types of activities.