The best approach for a supervisor to take when talking to an employee about unsatisfactory performance is to focus on how the performance can be improved.
Generally, people like to hear positive feedback. People do not like to hear negative feedback. So a good practice is to begin with what the employee did well. This “buttering up” of the employee puts a positive spin on the encounter. If you talk about all of the negatives and no positives, the person might become discouraged.
After focusing on the positive, reassure the employee that while there are performance areas where skill is lacking, the employee has shown potential for improvement. Be specific about what areas need improvement, and how that improvement can be made. For example, if an employee is often tardy to work, discuss why. Perhaps making the employees hours flexible or changing the time the employee comes in will help.