Most of the conflicts between tenants and landlords happen because of miscommunications. This is a letter that explains your rules and practices to the tenant. For example, it lets them know what happens if they pay the rent late. It tells them what to do in an emergency and much more.
This is a fillable form that you can email to yourself or both to yourself and your tenants before they move in. Here is a link to a Sample Letter, which you can copy and customize to fit your property and your rules.