Be sure your performance standards are in writing and create a consistent written warning system. Let employees know what is expected of them and the consequences of not meeting those expectations. Documentation is critical. With proper documentation and warnings, employees are less likely to sue, and you have a better defense.
I live in Arizona which is a right-to-work state, and that means that you can fire anybody anytime for any or no reason as long as you do not violate any employment discrimination laws. Even in a state with employer-favorable laws, however, firing an employee can still result in a wrongful termination lawsuit. Never fire an employee hastily or when you are angry.
Once you decide to fire the employee, take some time preparing and documenting the reasons for the termination. For example, if the employee