My professional theory is as basic as treating people as you wish to be treated. Lead through example (e.g., be on time and “present” for meetings; talk only when you have something of substance to say -- not every thought that you have is superior because you are in charge -- encourage others to express their ideas). Ensure that everyone fully understands his/her job and has the knowledge/training, tools, and encouragement to do that job.
Stay out of the way (i.e., do not micromanage and demotivate workers by making them feel powerless) and cross-train by offering plenty of opportunities to learn new skills or hone existing ones. Show people that you genuinely see and value their contributions by abundantly and publicly praising, recognizing and rewarding those who produce quality work reliably and who exhibit a ‘can do’ attitude. Assess traits that are holding people back and help them to see how to improve.
If you encourage people to take risks, be sure to let them know that you will support them -- even if they make a mistake. This is vital in my opinion.
Managers who do all of these things effectively don’t see excessive turnover. Of course, you will lose some ambitious people -- very often your most outstanding ones -- if you cannot offer them promotional opportunities. But if you are a capable leader, good people will always respect you and want to work with you; and even if they have to move on due to their family obligations or whatever, they will be happy to return to working with you if and when you have an opportunity available at their level.
Related: 5 Ways to Become a Better Manager