Being clear and concise in your company vision, and actively doing things that aligb with that. Not letting bad employees spoil good employees. It's less about the stuff you do, like tickets to sporting events, although fun, does not improve already meager moral and retention. Have people in management who actually care about the people they oversee, make sure they are trained to handle situations that arise like harassment or workers comp and be fair across the board. I have worked in HR and for tons of companies that had bad management but threw BBQ's regularly and while the food was nice it didn't make up for the problems at hand. I listened to employees, followed up with them, and did what I said I would.