A large part of having happy tenants is making sure they know exactly what to expect from the service they receive from you as a landlord. You should be careful to manage their expectations from the beginning of your landlord tenant relationship, so they know the important deadlines for anything that might be happening with their home, and they they feel comfortable and well informed.
Make sure your tenant has a copy of all terms and conditions in advance, and has a copy to keep. You should go through any points that are especially important to note, making sure they understand all their obligations. Check on your tenants every once in a while to make sure they are happy and have everything they need to be comfortable and happy. If they have any issues with the property, make sure they know who to tell so that it can be resolved for them.