Other than the aforementioned "Aim Small, Miss Small" and "Don't look at your pins, focus on the target," I would say my best tip was:
"Always end a shooting session, with a good shot!"
The thought behind this, is that you leave a positve subconscious impression which helps you remember what you did right instead of a negative which you may repeat. If I am having an off day, I will end my session a little early and at a closer range I am confident with in hitting a good group. Yesterday, that was a 2.5" - 40 yard group after a hell of a time correcting fletching contact and bad arrow flight.
~ERock