Your mind means knowing how you operate, how you are distracted, and how you concentrate. It is your "Trumpet Zen". You know when you in it because it seems like you remember all the right things to do when playing. You are relaxed, aware, ready to put your foot on the gas, and confident. Most of the great players I have observed all have one thing in common. They think about what they are doing at 100% capacity. NOTHING will pull them off of their "present time" task. Daily practice sets and routines greatly contribute to this habit. "Total Recall" of that moment (remembering when you played that lick perfectly) is part of it as well as having consistent muscle memory.