How do I improve my child's social skills?

Some kids are more introverted than others. My son is an introvert chap whereas my daughter is an extrovert. One cannot change the basic nature of the child but yes you can encourage him to make friends, ask him to participate in all the activities in class to develop public speaking and confidence, ask the teacher questions. Don't ever pressurize or compare him with other children. Each child is different. Encourage him to play with other kids in the park or your apartment in the evening. Invite his friends over at your place.