That is the big question!  

Let's rephrase the research to get a better understanding...

    1.     Praise. Don’t just say thank you. Tell them why you are saying thank you.  When you go to shake their hand at the end of a good day, bring your left hand around and cup the other side of their hand as say something like, “I really do appreciate your hard work on _____ today.”
    2.     Develop constantly and consistently.  This goes for the weakest employees as well as the great producers. Give them challenging tasks to help them get ready for promotion.  Make sure they know that is the reason you give them harder things to do.
    3.     Give the promotions out internally rather than look outside for new talent whenever possible.
    4.     Make leaders by giving leadership things to non-leaders.  When they complete the leadership task correctly, make sure everyone knows how great they did. Announce it at the next meeting or even at the water cooler.  In other words, shout it from the mountain top!
    5.     Ask for advice of your subordinates.  They will usually come up with the right answer. When they do let them know you agree and give them credit publicly for the solution.  Talk about intrinsic motivation.  If Mary thinks it is her idea, she will be the chief advocate of whatever it is, kind of like a mini-project manager.
    6.     Metrics, metrics, metrics.  Post metrics every day.  If employees know where they and others are performing, poor or great, they can self-motivate to improve or self-motivate to continue in current activity.  It is important to point out the goal line to ensure they understand at a glance exactly where they stand.
    7.     Communication is critical.  People who feel they are in the dark about what is going on suffer a drop in intrinsic motivation.  You need to treat your employees like partners.  Partners have very few secrets.