The secret is staying in shape not starting and stopping. It takes the same thing that is needed to be successful at anything individuals strive to achieve at. The key things are self discipline and self motivation. The key is getting up each day and getting it done. Lifting hard will go a long way to increase mental and emotional toughness.
Self doubt is one of the major causes for poor performance.
Every two weeks you should test players and while there are many good ways to test John Vargas and I set up a good testing program to see if players were really exercising and lifting on their own. We start them going to failure on chin ups giving them 15 second rest and going to failure again. 5 minutes rest and do bar dips to positive failur e 15 seconds rest and go again to positive failure. Bar dips is number of dips time body weight on the first set. The second sets are all much harder and give the tester a good idea of how well those tested can recover and deal with muscle pain.