Here are a few thoughts from Eric Werner in Brace Barber's No Excuse Leadership: Lessons from the US Army's Elite Rangers:
"Get as well prepared as possible...Stay in great shape."
"When they say you are going to run five miles, don't automatically prepare yourself mentally for a five-mile run."
"Stay mentally flexible."
"Be flexible and get mentally tough because no matter where your are in the school, you've got two options." (Either keep going or quit)
"Always expect more than the perceived requirements..."
"There are going to be all sorts of contingencies and things that are out of your control."
"...be aware that sometimes you going to have to react more than plan."
"You have to be responsible enough to set pride aside in deference to the mission."
"Trust you team and use your teammates to help the whole organization succeed."
"A real leader, even as a subordinate, will help the current leader by being self-motivated and going beyond the realm or his own responsibility."