The best thing you can do is communicate with them. Ask them about their career aspirations, take notes and see how you can assist them to achieve their goals with your business. Give feedback regularly during tool box talks about what people are doing well and what could be improved and how you can help them improve. These actions really help with loyalty. You can also do small things such as writing a personal thank you card, providing a bar b q after a big job is complete and so on. I hope this is helpful.