In our house cleaning company Superb Maids, employee engagement and motivation are super critical. Here are some of the things we do to stay in their good graces:

We care about their personal lives and development. If they are attending school, studying for another career, tending to their disabled kids, or have awesome hobbies, we are very supportive. We provide whatever time and space they need to devote to those pursuits.
We explain to them their larger mission: to give people clean homes and healthy, safe environments for their families. We give them an opportunity to contribute to our charitable pursuits. While we pay our staff for cleaning for cancer patients, for example, we let them know the company is performing the service as a charity, so they understand their awesome mission.
We maintain the pride in our work. Although the work is dirty, we give our staff snow-white polo shirts and beautiful navy aprons. We also give them metal golden badges, organized supplies, and nice business cards. We keep our internal standards of communication high and emphasize the quality and high standards all the time.
We hold our staff calmly accountable. If there is a performance issue, it's addressed directly and immediately. But not through raised voices or disrespectful tone. Rather, we clearly communicate our policies and outline the consequences for further violations. Usually, it's enough. But in those rare cases where it isn't, we make hard decisions, no matter how much we don't want to.
We have their backs. No matter what happens, our employees know we've got their backs. If there is a disrespectful client, difficult situation, or even a personal emergency, we step up to the plate and help. We don't leave one of our own out, hanging. Sometimes it means saying goodbye to lucrative clients. Or spending a non-trivial amount of money. But, it's worth it in the end.