Conduct a private one-on-one meeting with your defiant student. Approach this meeting with openness and humility. Allow the student to air any grievances they have with you as a teacher or a person. In this personal meeting, do not be defensive, but try your best to explain certain practices you have employed in the classroom.
Provide rationale for instructions and assignments. Oftentimes a student's defiance is a product of their inability to understand the relevance of classroom practices. This step is particularly important if your defiant student is a teenager or adult.
Modify assignments so that the defiant student can succeed. Often a student's defiance serves as their response to their perception of failure in the classroom. Modifying assignments can be perceived as demeaning if it is done on an individual basis. Therefore, modify assignments for the entire class to appeal to a defiant student's strengths. For example, if your defiant student is creative, provide an assignment in which the whole class can exercise their creativity. In addition to allowing the class a better chance to succeed, an assignment like this is more likely to draw the defiant student in.
Protect yourself from taking a student's defiant behavior personally. Often a student's defiant behavior is the product of a myriad of personal and social factors. Though good teachers are invested in their students, taking a student's defiance personally can damage your confidence as a teacher. Try your best to reach the student and educate them. If they remain unresponsive, move on and don't blame yourself.