My latest focus in running is relaxation. A body-audit, if you will.
Pick a body part that I shouldn't be engaging for running and ask myself if it's flexed or relaxed. Muscles you've identified as not helping, then ask yourself if it's relaxed. Try flexing then releasing. Pay attention to your running form, the sound of your steps, and your breathing.
Letting go of unneeded muscles will lower your heart/breathing rate, functioning economy improvements.
I have noticed I can incorporate this technique as I fall asleep. Its good practice for muscle relaxation while running. I noticed when I lay down to sleep my hands make tight'ish fists. Recognizing this and flattening out my hands changes my breathing and increases relaxation. Flex a foot then relax it. Notices the difference? Flex gastric chain then relax it. Notice Tue difference. Turning off everything allows sweet sleep. Relaxing most things allows for sweet runs.
* This topic supports my theory that the key to endurance is not ability to engage muscles but is the ability to relax muscles. Extrapolated explains a cramp-inability to release a completely flexed muscle. Watching heart rate creep to maintain the same intensity is due to recruiting muscles you don't need for the motion.