Training hard means maximizing your effort while avoiding overtraining. You train within yourself, doing what you're capable of doing and then slightly more. It's the slightly-more part that results in the strength gains, the endurance gains, and the speed gains. Training smart means paying attention to what's happening in your body as you train. It requires focus and repetition.
Visualization is an important part of focus.
If you're weight-lifting, visualize the prime mover for that exercise, the muscle for which the exercise is designed. The prime mover for the bench press is the pectoralis group. The prime mover for military presses is the deltoid. When you're running, visualize a straight, yet fluid spine and strong abdominal muscles. Your head is erect and your chest is open.