You incorporate the mind-muscle link when tuning into the particular muscle involved in an exercise and being aware of how the muscle feels.  The key is learning how the muscles within your body are activated when moving.  For example, your pectoralis muscle (chest) stretches and contracts when performing the flye movement.   In order to become more aware of how your pecs are activated, try stepping just past an open doorway with arms outstretched.  Now press your hands against the open door frame.  You should feel a tensing of your chest muscles.  Utilize this awareness of how your chest feels when performing the flye movement.  The feeling experienced when pressing in an open doorway compared to executing the flye exercise  is coalesced by your mind.  Congratulations, you've just made a mind-muscle link with regard to activating your chest muscle during a flye movement. 

     Success at achieving your fitness goal is ultimately dependent on how your mind perceives the goal.  Think of the goal as something that will be achieved rather than that which might be achieved.   Mental skills such as positive attitude, visualization, confidence, focus, and performance preparation are techniques used by athletes when they train and compete in order to improve performance.    
     Positive attitude is paramount since your performance largely depends on your thoughts and emotions.  If you don't think you can do a 240-lb deadlift, you won't.  It's that simple.   You must think positively in accomplishing your goal and block out any negative thoughts.  Be aware of your thoughts and feelings and take charge of them by eliminating negative self-talk, leaving only positive thoughts remaining.  
     Visualization (or mental imagery) is imagining in your mind the act of performing the act (right down to the movement patterns) that will allow you to accomplish your goal.  Neuromuscular innervation occurs when the mind imagines the movement and the muscles perceive it.  After the muscles perceive the movement, muscle memory can begin to occur.  Later, when the movement has been performed, the muscles of the body will "remember" the movement and how it felt when performing it.  Close your eyes, relax and focus on performing the act.  Imagine performing the act in your mind and perceive what it  feels and looks like before actually doing it.  Imagine performing the movement over and over in your mind's eye until you're completely confident you will be successful and then do it.
     Confidence is absolutely necessary to be successful in accomplishing your goal.  This means there should be no doubt, an unshakable self-belief,  that you will succeed.  Remember past experiences and how you accomplished particular goals and how great it felt.  By reliving these moments, you build self-confidence to perform new goals.
      Focus entails visualizing important details of the performance of your goal.  Intense concentration with laser-like focus is what gets the job done.  Close your eyes if necessary to minimize any environmental distractions from disrupting your focus.  Be in control of your thoughts, emotions and actions.
     Performance preparation means wearing the right gear (clothes), playing the right music (for inspiration), and readying yourself for the mission at hand.  
     After applying these techniques on a regular basis in your training you will not only become successful in accomplishing any goal, but you will also take pleasure in succeeding.  Think positive thoughts, be persistent in your training, and most of all, be mentally tough.   Then you will come to realize the power of the mind in accomplishing any goal or endeavor!