A mantra is a sound, syllable, word, or group of words that is considered capable of "creating transformation." In the last couple years, I created "transformation" in my running - from heel striking to mid-foot landing. I also gained much more trail running experience. This can be done through good coaching, practice and mantras.
When my main goal was to increase cadence, my mantra for weeks was 'tap-tap-tap-tap..' said to the tune of 23 right foots in 15 seconds.
When I noticed I was spending energy forcing my foot to the ground instead of letting it fall, my mantra became 'lift-lift-lift...' Lift-lift also works for reminding me to lift my foot up as fast as I can on downhill. In the woods, lifting quickly helps prevent losing traction, and on the roads prevents unintended braking.
**HAHA, in the middle of an ultra, I borrow from Finding Nemo with "Just keep running, just keep running." Thanks, Ellen, for seeing me through some tough races :).
Try this one: "light-quick-steps-lift, lift, lift' to help maintain a quick cadence and minimize the time your feet are on the ground - both key cues in barefoot running.
What are some of the things you repeat to yourself (or...out loud, I guess)?
More on Mantras at Runner's World.